diff --git a/apps/dav/lib/CalDAV/TipBroker.php b/apps/dav/lib/CalDAV/TipBroker.php
index 629b4fde13c..82a00171dfa 100644
--- a/apps/dav/lib/CalDAV/TipBroker.php
+++ b/apps/dav/lib/CalDAV/TipBroker.php
@@ -9,6 +9,7 @@ declare(strict_types=1);
 
 namespace OCA\DAV\CalDAV;
 
+use Sabre\VObject\Component;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\ITip\Broker;
 use Sabre\VObject\ITip\Message;
@@ -27,9 +28,56 @@ class TipBroker extends Broker {
 		'SUMMARY',
 		'DESCRIPTION',
 		'LOCATION',
-
 	];
 
+	/**
+	 * Processes incoming CANCEL messages.
+	 *
+	 * This is a message from an organizer, and means that either an
+	 * attendee got removed from an event, or an event got cancelled
+	 * altogether.
+	 *
+	 * @param VCalendar $existingObject
+	 *
+	 * @return VCalendar|null
+	 */
+	protected function processMessageCancel(Message $itipMessage, ?VCalendar $existingObject = null) {
+		if ($existingObject === null) {
+			return null;
+		}
+
+		$componentType = $itipMessage->component;
+		$instances = [];
+
+		foreach ($itipMessage->message->$componentType as $component) {
+			$instanceId = isset($component->{'RECURRENCE-ID'}) ? $component->{'RECURRENCE-ID'}->getValue() : 'base';
+			$instances[$instanceId] = $component;
+		}
+		// any existing instances should be marked as cancelled
+		foreach ($existingObject->$componentType as $component) {
+			$instanceId = isset($component->{'RECURRENCE-ID'}) ? $component->{'RECURRENCE-ID'}->getValue() : 'base';
+			if (isset($instances[$instanceId])) {
+				if (isset($component->STATUS)) {
+					$component->STATUS->setValue('CANCELLED');
+				} else {
+					$component->add('STATUS', 'CANCELLED');
+				}
+				if (isset($component->SEQUENCE)) {
+					$component->SEQUENCE->setValue($itipMessage->sequence);
+				} else {
+					$component->add('SEQUENCE', $itipMessage->sequence);
+				}
+				unset($instances[$instanceId]);
+			}
+		}
+		// any remaining instances are new and should be added
+		foreach ($instances as $instance) {
+			$existingObject->add($instance);
+		}
+
+		return $existingObject;
+	}
+
 	/**
 	 * This method is used in cases where an event got updated, and we
 	 * potentially need to send emails to attendees to let them know of updates
@@ -38,154 +86,219 @@ class TipBroker extends Broker {
 	 * We will detect which attendees got added, which got removed and create
 	 * specific messages for these situations.
 	 *
-	 * @return array
+	 * @return array<int,Message>
 	 */
 	protected function parseEventForOrganizer(VCalendar $calendar, array $eventInfo, array $oldEventInfo) {
-		// Merging attendee lists.
-		$attendees = [];
-		foreach ($oldEventInfo['attendees'] as $attendee) {
-			$attendees[$attendee['href']] = [
-				'href' => $attendee['href'],
-				'oldInstances' => $attendee['instances'],
-				'newInstances' => [],
-				'name' => $attendee['name'],
-				'forceSend' => null,
-			];
-		}
-		foreach ($eventInfo['attendees'] as $attendee) {
-			if (isset($attendees[$attendee['href']])) {
-				$attendees[$attendee['href']]['name'] = $attendee['name'];
-				$attendees[$attendee['href']]['newInstances'] = $attendee['instances'];
-				$attendees[$attendee['href']]['forceSend'] = $attendee['forceSend'];
-			} else {
-				$attendees[$attendee['href']] = [
-					'href' => $attendee['href'],
-					'oldInstances' => [],
-					'newInstances' => $attendee['instances'],
-					'name' => $attendee['name'],
-					'forceSend' => $attendee['forceSend'],
-				];
-			}
-		}
 
 		$messages = [];
 
+		// construct template calendar from original calendar without components
+		$template = new VCalendar();
+		foreach ($template->children() as $property) {
+			$template->remove($property);
+		}
+		foreach ($calendar->children() as $property) {
+			if (in_array($property->name, ['METHOD', 'VEVENT', 'VTODO', 'VJOURNAL', 'VFREEBUSY'], true) === false) {
+				$template->add(clone $property);
+			}
+		}
+		// extract event information
+		$objectId = $eventInfo['uid'];
+		if ($calendar->getBaseComponent() === null) {
+			$objectType = $calendar->getComponents()[0]->name;
+		} else {
+			$objectType = $calendar->getBaseComponent()->name;
+		}
+		$objectSequence = $eventInfo['sequence'] ?? 1;
+		$organizerHref = $eventInfo['organizer'] ?? $oldEventInfo['organizer'];
+		if ($eventInfo['organizerName'] instanceof \Sabre\VObject\Parameter) {
+			$organizerName = $eventInfo['organizerName']->getValue();
+		} else {
+			$organizerName = $eventInfo['organizerName'];
+		}
+		// detect if the singleton or recurring base instance was converted to non-scheduling
+		if (count($eventInfo['instances']) === 0 && count($oldEventInfo['instances']) > 0) {
+			foreach ($oldEventInfo['attendees'] as $attendee) {
+				$messages[] = $this->generateMessage(
+					$oldEventInfo['instances'], $organizerHref, $organizerName, $attendee, $objectId, $objectType, $objectSequence, 'CANCEL', $template
+				);
+			}
+			return $messages;
+		}
+		// detect if the singleton or recurring base instance was cancelled
+		if ($eventInfo['instances']['master']?->STATUS?->getValue() === 'CANCELLED' && $oldEventInfo['instances']['master']?->STATUS?->getValue() !== 'CANCELLED') {
+			foreach ($eventInfo['attendees'] as $attendee) {
+				$messages[] = $this->generateMessage(
+					$eventInfo['instances'], $organizerHref, $organizerName, $attendee, $objectId, $objectType, $objectSequence, 'CANCEL', $template
+				);
+			}
+			return $messages;
+		}
+		// detect if a new cancelled instance was created
+		$cancelledNewInstances = [];
+		if (isset($oldEventInfo['instances'])) {
+			$instancesDelta = array_diff_key($eventInfo['instances'], $oldEventInfo['instances']);
+			foreach ($instancesDelta as $id => $instance) {
+				if ($instance->STATUS?->getValue() === 'CANCELLED') {
+					$cancelledNewInstances[] = $id;
+					foreach ($eventInfo['attendees'] as $attendee) {
+						$messages[] = $this->generateMessage(
+							[$id => $instance], $organizerHref, $organizerName, $attendee, $objectId, $objectType, $objectSequence, 'CANCEL', $template
+						);
+					}
+				}
+			}
+		}
+		// detect attendee mutations
+		$attendees = array_unique(
+			array_merge(
+				array_keys($eventInfo['attendees']),
+				array_keys($oldEventInfo['attendees'])
+			)
+		);
 		foreach ($attendees as $attendee) {
-			// An organizer can also be an attendee. We should not generate any
-			// messages for those.
-			if ($attendee['href'] === $eventInfo['organizer']) {
+			// Skip organizer
+			if ($attendee === $organizerHref) {
 				continue;
 			}
 
-			$message = new Message();
-			$message->uid = $eventInfo['uid'];
-			$message->component = 'VEVENT';
-			$message->sequence = $eventInfo['sequence'];
-			$message->sender = $eventInfo['organizer'];
-			$message->senderName = $eventInfo['organizerName'];
-			$message->recipient = $attendee['href'];
-			$message->recipientName = $attendee['name'];
+			// Skip if SCHEDULE-AGENT=CLIENT (respect RFC 6638)
+			if ($this->scheduleAgentServerRules
+				&& isset($eventInfo['attendees'][$attendee]['scheduleAgent'])
+				&& strtoupper($eventInfo['attendees'][$attendee]['scheduleAgent']) === 'CLIENT') {
+				continue;
+			}
 
-			// Creating the new iCalendar body.
-			$icalMsg = new VCalendar();
+			// detect if attendee was removed and send cancel message
+			if (!isset($eventInfo['attendees'][$attendee]) && isset($oldEventInfo['attendees'][$attendee])) {
+				//get all instances of the attendee was removed from.
+				$instances = array_intersect_key($oldEventInfo['instances'], array_flip(array_keys($oldEventInfo['attendees'][$attendee]['instances'])));
+				$messages[] = $this->generateMessage(
+					$instances, $organizerHref, $organizerName, $oldEventInfo['attendees'][$attendee], $objectId, $objectType, $objectSequence, 'CANCEL', $template
+				);
+				continue;
+			}
+			// otherwise any created or modified instances will be sent as REQUEST
+			$instances = array_intersect_key($eventInfo['instances'], array_flip(array_keys($eventInfo['attendees'][$attendee]['instances'])));
 
-			foreach ($calendar->select('VTIMEZONE') as $timezone) {
-				$icalMsg->add(clone $timezone);
+			// Remove already-cancelled new instances from REQUEST
+			if (!empty($cancelledNewInstances)) {
+				$instances = array_diff_key($instances, array_flip($cancelledNewInstances));
 			}
-			// If there are no instances the attendee is a part of, it means
-			// the attendee was removed and we need to send them a CANCEL message.
-			// Also If the meeting STATUS property was changed to CANCELLED
-			// we need to send the attendee a CANCEL message.
-			if (!$attendee['newInstances'] || $eventInfo['status'] === 'CANCELLED') {
-
-				$message->method = $icalMsg->METHOD = 'CANCEL';
-				$message->significantChange = true;
-				// clone base event
-				if (isset($eventInfo['instances']['master'])) {
-					$event = clone $eventInfo['instances']['master'];
-				} else {
-					$event = clone $oldEventInfo['instances']['master'];
-				}
-				// alter some properties
-				unset($event->ATTENDEE);
-				$event->add('ATTENDEE', $attendee['href'], ['CN' => $attendee['name'],]);
-				$event->DTSTAMP = gmdate('Ymd\\THis\\Z');
-				$event->SEQUENCE = $message->sequence;
-				$icalMsg->add($event);
-
-			} else {
-				// The attendee gets the updated event body
-				$message->method = $icalMsg->METHOD = 'REQUEST';
-
-				// We need to find out that this change is significant. If it's
-				// not, systems may opt to not send messages.
-				//
-				// We do this based on the 'significantChangeHash' which is
-				// some value that changes if there's a certain set of
-				// properties changed in the event, or simply if there's a
-				// difference in instances that the attendee is invited to.
-
-				$oldAttendeeInstances = array_keys($attendee['oldInstances']);
-				$newAttendeeInstances = array_keys($attendee['newInstances']);
-
-				$message->significantChange
-					= $attendee['forceSend'] === 'REQUEST'
-					|| count($oldAttendeeInstances) !== count($newAttendeeInstances)
-					|| count(array_diff($oldAttendeeInstances, $newAttendeeInstances)) > 0
-					|| $oldEventInfo['significantChangeHash'] !== $eventInfo['significantChangeHash'];
-
-				foreach ($attendee['newInstances'] as $instanceId => $instanceInfo) {
-					$currentEvent = clone $eventInfo['instances'][$instanceId];
-					if ($instanceId === 'master') {
-						// We need to find a list of events that the attendee
-						// is not a part of to add to the list of exceptions.
-						$exceptions = [];
-						foreach ($eventInfo['instances'] as $instanceId => $vevent) {
-							if (!isset($attendee['newInstances'][$instanceId])) {
-								$exceptions[] = $instanceId;
-							}
-						}
-
-						// If there were exceptions, we need to add it to an
-						// existing EXDATE property, if it exists.
-						if ($exceptions) {
-							if (isset($currentEvent->EXDATE)) {
-								$currentEvent->EXDATE->setParts(array_merge(
-									$currentEvent->EXDATE->getParts(),
-									$exceptions
-								));
-							} else {
-								$currentEvent->EXDATE = $exceptions;
-							}
-						}
-
-						// Cleaning up any scheduling information that
-						// shouldn't be sent along.
-						unset($currentEvent->ORGANIZER['SCHEDULE-FORCE-SEND']);
-						unset($currentEvent->ORGANIZER['SCHEDULE-STATUS']);
-
-						foreach ($currentEvent->ATTENDEE as $attendee) {
-							unset($attendee['SCHEDULE-FORCE-SEND']);
-							unset($attendee['SCHEDULE-STATUS']);
-
-							// We're adding PARTSTAT=NEEDS-ACTION to ensure that
-							// iOS shows an "Inbox Item"
-							if (!isset($attendee['PARTSTAT'])) {
-								$attendee['PARTSTAT'] = 'NEEDS-ACTION';
-							}
-						}
+
+			// Skip if no instances left to send
+			if (empty($instances)) {
+				continue;
+			}
+
+			// Add EXDATE for instances the attendee is NOT part of (only for recurring events with master)
+			if (isset($instances['master']) && count($eventInfo['instances']) > 1) {
+				$masterInstance = clone $instances['master'];
+				$excludedDates = [];
+
+				foreach ($eventInfo['instances'] as $instanceId => $instance) {
+					if ($instanceId !== 'master' && !isset($eventInfo['attendees'][$attendee]['instances'][$instanceId])) {
+						$excludedDates[] = $instance->{'RECURRENCE-ID'}->getValue();
 					}
+				}
 
-					$currentEvent->DTSTAMP = gmdate('Ymd\\THis\\Z');
-					$icalMsg->add($currentEvent);
+				if (!empty($excludedDates)) {
+					if (isset($masterInstance->EXDATE)) {
+						$currentExdates = $masterInstance->EXDATE->getParts();
+						$masterInstance->EXDATE->setParts(array_merge($currentExdates, $excludedDates));
+					} else {
+						$masterInstance->EXDATE = $excludedDates;
+					}
+					$instances['master'] = $masterInstance;
 				}
 			}
 
-			$message->message = $icalMsg;
-			$messages[] = $message;
+			$messages[] = $this->generateMessage(
+				$instances, $organizerHref, $organizerName, $eventInfo['attendees'][$attendee], $objectId, $objectType, $objectSequence, 'REQUEST', $template
+			);
 		}
 
 		return $messages;
 	}
 
+	/**
+	 * Generates an iTip message for a specific attendee
+	 *
+	 * @param array<string, Component> $instances Array of event instances to include, keyed by instance ID:
+	 *                                            - 'master' => Component: The master/base event
+	 *                                            - '{RECURRENCE-ID}' => Component: Exception instances
+	 * @param string $organizerHref The organizer's calendar-user address (e.g., 'mailto:user@example.com')
+	 * @param string|null $organizerName The organizer's display name
+	 * @param array $attendee The attendee information containing:
+	 *                        - 'href' (string): The attendee's calendar-user address
+	 *                        - 'name' (string): The attendee's display name
+	 *                        - 'scheduleAgent' (string|null): SCHEDULE-AGENT parameter
+	 *                        - 'instances' (array): Instances this attendee is part of
+	 * @param string $objectId The UID of the event
+	 * @param string $objectType The component type ('VEVENT', 'VTODO', etc.)
+	 * @param int $objectSequence The sequence number of the event
+	 * @param string $method The iTip method ('REQUEST', 'CANCEL', 'REPLY', etc.)
+	 * @param VCalendar $template The template calendar object (without event components)
+	 * @return Message The generated iTip message ready to be sent
+	 */
+	protected function generateMessage(
+		array $instances,
+		string $organizerHref,
+		?string $organizerName,
+		array $attendee,
+		string $objectId,
+		string $objectType,
+		int $objectSequence,
+		string $method,
+		VCalendar $template,
+	): Message {
+
+		$recipientAddress = $attendee['href'] ?? '';
+		$recipientName = $attendee['name'] ?? '';
+
+		$vObject = clone $template;
+		if ($vObject->METHOD && $vObject->METHOD->getValue() !== $method) {
+			$vObject->METHOD->setValue($method);
+		} else {
+			$vObject->add('METHOD', $method);
+		}
+		foreach ($instances as $instance) {
+			$vObject->add($this->componentSanitizeScheduling(clone $instance));
+		}
+
+		$message = new Message();
+		$message->method = $method;
+		$message->uid = $objectId;
+		$message->component = $objectType;
+		$message->sequence = $objectSequence;
+		$message->sender = $organizerHref;
+		$message->senderName = $organizerName;
+		$message->recipient = $recipientAddress;
+		$message->recipientName = $recipientName;
+		$message->significantChange = true;
+		$message->message = $vObject;
+
+		return $message;
+
+	}
+
+	protected function componentSanitizeScheduling(Component $component): Component {
+		// Cleaning up any scheduling information that should not be sent or is missing
+		unset($component->ORGANIZER['SCHEDULE-FORCE-SEND'], $component->ORGANIZER['SCHEDULE-STATUS']);
+		foreach ($component->ATTENDEE as $attendee) {
+			unset($attendee['SCHEDULE-FORCE-SEND'], $attendee['SCHEDULE-STATUS']);
+
+			if (!isset($attendee['PARTSTAT'])) {
+				$attendee['PARTSTAT'] = 'NEEDS-ACTION';
+			}
+		}
+		// Sequence is a required property, default is 0
+		// https://datatracker.ietf.org/doc/html/rfc5545#section-3.8.7.4
+		if ($component->SEQUENCE === null) {
+			$component->add('SEQUENCE', 0);
+		}
+
+		return $component;
+	}
+
 }
diff --git a/apps/dav/tests/unit/CalDAV/TipBrokerTest.php b/apps/dav/tests/unit/CalDAV/TipBrokerTest.php
index ddf992767d6..88438950125 100644
--- a/apps/dav/tests/unit/CalDAV/TipBrokerTest.php
+++ b/apps/dav/tests/unit/CalDAV/TipBrokerTest.php
@@ -15,11 +15,19 @@ class TipBrokerTest extends TestCase {
 
 	private TipBroker $broker;
 	private VCalendar $vCalendar1a;
+	private VCalendar $vCalendar2a;
+	private array $templateEventInfo;
 
 	protected function setUp(): void {
 		parent::setUp();
 
 		$this->broker = new TipBroker();
+
+		$this->templateEventInfo = [
+			'organizer' => null,
+			'attendees' => [],
+			'significantChangeHash' => '',
+		];
 		// construct calendar with a 1 hour event and same start/end time zones
 		$this->vCalendar1a = new VCalendar();
 		/** @var VEvent $vEvent */
@@ -28,7 +36,7 @@ class TipBrokerTest extends TestCase {
 		$vEvent->add('DTSTAMP', '20240701T000000Z');
 		$vEvent->add('CREATED', '20240701T000000Z');
 		$vEvent->add('LAST-MODIFIED', '20240701T000000Z');
-		$vEvent->add('SEQUENCE', '1');
+		$vEvent->add('SEQUENCE', 1);
 		$vEvent->add('STATUS', 'CONFIRMED');
 		$vEvent->add('DTSTART', '20240701T080000', ['TZID' => 'America/Toronto']);
 		$vEvent->add('DTEND', '20240701T090000', ['TZID' => 'America/Toronto']);
@@ -41,140 +49,534 @@ class TipBrokerTest extends TestCase {
 			'ROLE' => 'REQ-PARTICIPANT',
 			'RSVP' => 'TRUE'
 		]);
-	}
 
-	public function testParseEventForOrganizerOnCreate(): void {
+		// construct calendar with a 1 hour event and same start/end time zones
+		// recurring every week on Monday for 12 weeks
+		$this->vCalendar2a = new VCalendar();
+		/** @var VEvent $vEvent */
+		$vEvent = $this->vCalendar2a->add('VEVENT', []);
+		$vEvent->add('UID', '96a0e6b1-d886-4a55-a60d-152b31401dcc');
+		$vEvent->add('DTSTAMP', '20240701T000000Z');
+		$vEvent->add('CREATED', '20240701T000000Z');
+		$vEvent->add('LAST-MODIFIED', '20240701T000000Z');
+		$vEvent->add('SEQUENCE', 1);
+		$vEvent->add('STATUS', 'CONFIRMED');
+		$vEvent->add('DTSTART', '20240701T080000', ['TZID' => 'America/Toronto']);
+		$vEvent->add('DTEND', '20240701T090000', ['TZID' => 'America/Toronto']);
+		$vEvent->add('RRULE', 'FREQ=WEEKLY;COUNT=12;BYDAY=MO');
+		$vEvent->add('SUMMARY', 'Test Event');
+		$vEvent->add('ORGANIZER', 'mailto:organizer@testing.com', ['CN' => 'Organizer']);
+		$vEvent->add('ATTENDEE', 'mailto:attendee1@testing.com', [
+			'CN' => 'Attendee One',
+			'CUTYPE' => 'INDIVIDUAL',
+			'PARTSTAT' => 'NEEDS-ACTION',
+			'ROLE' => 'REQ-PARTICIPANT',
+			'RSVP' => 'TRUE'
+		]);
+	}
 
+	/**
+	 * Tests user creating a new singleton or recurring event
+	 */
+	public function testParseEventForOrganizerCreated(): void {
 		// construct calendar and generate event info for newly created event with one attendee
-		$calendar = clone $this->vCalendar1a;
-		$previousEventInfo = [
-			'organizer' => null,
-			'significantChangeHash' => '',
-			'attendees' => [],
-		];
-		$currentEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
+		$mutatedCalendar = clone $this->vCalendar1a;
+		$originalEventInfo = $this->templateEventInfo;
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
 		// test iTip generation
-		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$calendar, $currentEventInfo, $previousEventInfo]);
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
 		$this->assertCount(1, $messages);
 		$this->assertEquals('REQUEST', $messages[0]->method);
-		$this->assertEquals($calendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
-		$this->assertEquals($calendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+	}
 
+	/**
+	 * Tests user modifying an existing singleton or recurring (base) event
+	 */
+	public function testParseEventForOrganizerModified(): void {
+		// construct calendar and generate event info for modified event with one attendee
+		$originalCalendar = clone $this->vCalendar1a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $this->vCalendar1a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedCalendar->VEVENT->SUMMARY->setValue('Test Event Modified');
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(1, $messages);
+		$this->assertEquals('REQUEST', $messages[0]->method);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
 	}
 
-	public function testParseEventForOrganizerOnModify(): void {
+	/**
+	 * Tests user deleting an existing singleton or recurring (base) event
+	 */
+	public function testParseEventForOrganizerDeleted(): void {
+		// construct calendar and generate event info for modified event with one attendee
+		$originalCalendar = clone $this->vCalendar1a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedEventInfo = $originalEventInfo;
+		$mutatedEventInfo['attendees'] = [];
+		++$mutatedEventInfo['sequence'];
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$originalCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(1, $messages);
+		$this->assertEquals('CANCEL', $messages[0]->method);
+		$this->assertEquals($originalCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($originalCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+	}
 
+	/**
+	 * Tests user cancelling an existing singleton or recurring (base) event
+	 */
+	public function testParseEventForOrganizerStatusCancelled(): void {
 		// construct calendar and generate event info for modified event with one attendee
-		$calendar = clone $this->vCalendar1a;
-		$previousEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
-		$calendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
-		$calendar->VEVENT->SEQUENCE->setValue(2);
-		$calendar->VEVENT->SUMMARY->setValue('Test Event Modified');
-		$currentEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
-		// test iTip generation
-		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$calendar, $currentEventInfo, $previousEventInfo]);
+		$originalCalendar = clone $this->vCalendar1a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $this->vCalendar1a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedCalendar->VEVENT->STATUS->setValue('CANCELLED');
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
 		$this->assertCount(1, $messages);
+		$this->assertEquals('CANCEL', $messages[0]->method);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+	}
+
+	/**
+	 * Tests user adding an attendee to an existing singleton or recurring (base) event
+	 */
+	public function testParseEventForOrganizerAddAttendee(): void {
+		// construct calendar and generate event info for modified event with two attendees
+		$originalCalendar = clone $this->vCalendar1a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $this->vCalendar1a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedCalendar->VEVENT->add('ATTENDEE', 'mailto:attendee2@testing.com', [
+			'CN' => 'Attendee Two',
+			'CUTYPE' => 'INDIVIDUAL',
+			'PARTSTAT' => 'NEEDS-ACTION',
+			'ROLE' => 'REQ-PARTICIPANT',
+			'RSVP' => 'TRUE'
+		]);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		// attendee modifications get generated in order of Added, Removed, Existing
+		$this->assertCount(2, $messages);
 		$this->assertEquals('REQUEST', $messages[0]->method);
-		$this->assertEquals($calendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
-		$this->assertEquals($calendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertEquals('REQUEST', $messages[1]->method);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[1]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE[1]->getValue(), $messages[1]->recipient);
+	}
 
+	/**
+	 * Tests user removing an attendee from an existing singleton or recurring (base) event
+	 */
+	public function testParseEventForOrganizerRemoveAttendee(): void {
+		// construct calendar and generate event info for modified event with two attendees
+		$originalCalendar = clone $this->vCalendar1a;
+		$originalCalendar->VEVENT->add('ATTENDEE', 'mailto:attendee2@testing.com', [
+			'CN' => 'Attendee Two',
+			'CUTYPE' => 'INDIVIDUAL',
+			'PARTSTAT' => 'NEEDS-ACTION',
+			'ROLE' => 'REQ-PARTICIPANT',
+			'RSVP' => 'TRUE'
+		]);
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $this->vCalendar1a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedCalendar->VEVENT->remove('ATTENDEE');
+		$mutatedCalendar->VEVENT->add('ATTENDEE', 'mailto:attendee1@testing.com', [
+			'CN' => 'Attendee One',
+			'CUTYPE' => 'INDIVIDUAL',
+			'PARTSTAT' => 'NEEDS-ACTION',
+			'ROLE' => 'REQ-PARTICIPANT',
+			'RSVP' => 'TRUE'
+		]);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		// attendee modifications get generated in order of Added, Removed, Existing
+		$this->assertCount(2, $messages);
+		$this->assertEquals('REQUEST', $messages[0]->method);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertEquals('CANCEL', $messages[1]->method);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[1]->sender);
+		$this->assertEquals('mailto:attendee2@testing.com', $messages[1]->recipient);
 	}
 
-	public function testParseEventForOrganizerOnDelete(): void {
 
-		// construct calendar and generate event info for modified event with one attendee
-		$calendar = clone $this->vCalendar1a;
-		$previousEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
-		$currentEventInfo = $previousEventInfo;
-		$currentEventInfo['attendees'] = [];
-		++$currentEventInfo['sequence'];
+	/**
+	 * Tests user converts existing singleton or recurring (base) event from attended to attendeless
+	 */
+	public function testParseEventForOrganizerRemoveOrganizerAndAttendees(): void {
+		// construct calendar and generate event info for modified event with two attendees
+		$originalCalendar = clone $this->vCalendar1a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedCalendar = clone $this->vCalendar1a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedCalendar->VEVENT->remove('ORGANIZER');
+		$mutatedCalendar->VEVENT->remove('ATTENDEE');
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
 		// test iTip generation
-		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$calendar, $currentEventInfo, $previousEventInfo]);
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		// attendee modifications get generated in order of Added, Removed, Existing
 		$this->assertCount(1, $messages);
 		$this->assertEquals('CANCEL', $messages[0]->method);
-		$this->assertEquals($calendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
-		$this->assertEquals($calendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertEquals(2, $messages[0]->sequence);
+		$this->assertEquals($originalCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($originalCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+	}
+
+	/**
+	 * Tests user modifying recurring (base) event by moving instance to a new date
+	 */
+	public function testParseEventForOrganizerCreatedInstance(): void {
+		// construct calendar and generate event info for modified event with two attendees
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedInstance = clone $originalCalendar->VEVENT;
+		$mutatedInstance->add('RECURRENCE-ID', '20240715T080000', ['TZID' => 'America/Toronto']);
+		$mutatedInstance->SEQUENCE->setValue(0);
+		$mutatedInstance->DTSTART->setValue('20240717T080000');
+		$mutatedInstance->DTEND->setValue('20240717T090000');
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->add($mutatedInstance);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		// attendee modifications get generated in order of Added, Removed, Existing
+		$this->assertCount(1, $messages);
+		$this->assertEquals('REQUEST', $messages[0]->method);
+		$this->assertEquals(1, $messages[0]->sequence);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertCount(2, $messages[0]->message->VEVENT);
+		$this->assertEquals('20240715T080000', $messages[0]->message->VEVENT[1]->{'RECURRENCE-ID'}->getValue());
 
 	}
 
-	public function testParseEventForOrganizerOnStatusCancelled(): void {
+	/**
+	 * Tests user modifying recurring (base) event by cancelling a single instance
+	 */
+	public function testParseEventForOrganizerCreatedInstanceCancelled(): void {
+		// construct calendar and generate event info for modified event with two attendees
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedInstance = clone $originalCalendar->VEVENT;
+		$mutatedInstance->add('RECURRENCE-ID', '20240715T080000', ['TZID' => 'America/Toronto']);
+		$mutatedInstance->SEQUENCE->setValue(0);
+		$mutatedInstance->STATUS->setValue('CANCELLED');
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->add($mutatedInstance);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		// attendee modifications get generated in order of Added, Removed, Existing
+		$this->assertCount(2, $messages);
+		$this->assertEquals('CANCEL', $messages[0]->method);
+		$this->assertEquals(1, $messages[0]->sequence);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertCount(1, $messages[0]->message->VEVENT);
+		$this->assertEquals('20240715T080000', $messages[0]->message->VEVENT->{'RECURRENCE-ID'}->getValue());
+
+	}
 
-		// construct calendar and generate event info for modified event with one attendee
-		$calendar = clone $this->vCalendar1a;
-		$previousEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
-		$calendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
-		$calendar->VEVENT->SEQUENCE->setValue(2);
-		$calendar->VEVENT->STATUS->setValue('CANCELLED');
-		$currentEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
-		// test iTip generation
-		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$calendar, $currentEventInfo, $previousEventInfo]);
+	/**
+	 * Tests user modifying recurring (instance) event with non status or attendee changes
+	 */
+	public function testParseEventForOrganizerModifyInstance(): void {
+		// construct calendar and generate event info for modified event with two attendees
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalInstance = clone $originalCalendar->VEVENT;
+		$originalInstance->add('RECURRENCE-ID', '20240715T080000', ['TZID' => 'America/Toronto']);
+		$originalInstance->SEQUENCE->setValue(1);
+		$originalInstance->DTSTART->setValue('20240717T080000');
+		$originalInstance->DTEND->setValue('20240717T090000');
+		$originalCalendar->add($originalInstance);
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+
+		$mutatedInstance = clone $originalInstance;
+		$mutatedInstance->SEQUENCE->setValue(2);
+		$mutatedInstance->DTSTART->setValue('20240718T080000');
+		$mutatedInstance->DTEND->setValue('20240718T090000');
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->add($mutatedInstance);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		// attendee modifications get generated in order of Added, Removed, Existing
 		$this->assertCount(1, $messages);
-		$this->assertEquals('CANCEL', $messages[0]->method);
-		$this->assertEquals($calendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
-		$this->assertEquals($calendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertEquals('REQUEST', $messages[0]->method);
+		$this->assertEquals(1, $messages[0]->sequence);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertCount(2, $messages[0]->message->VEVENT);
+		$this->assertEquals('20240715T080000', $messages[0]->message->VEVENT[1]->{'RECURRENCE-ID'}->getValue());
 
 	}
 
-	public function testParseEventForOrganizerOnAddAttendee(): void {
+	/**
+	 * Tests user modifying recurring (instance) event by setting status to cancelled
+	 */
+	public function testParseEventForOrganizerModifyInstanceStatus(): void {
+		// construct calendar and generate event info for modified event with two attendees
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalInstance = clone $originalCalendar->VEVENT;
+		$originalInstance->add('RECURRENCE-ID', '20240715T080000', ['TZID' => 'America/Toronto']);
+		$originalInstance->SEQUENCE->setValue(1);
+		$originalInstance->DTSTART->setValue('20240717T080000');
+		$originalInstance->DTEND->setValue('20240717T090000');
+		$originalCalendar->add($originalInstance);
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedInstance = clone $originalInstance;
+		$mutatedInstance->SEQUENCE->setValue(2);
+		$mutatedInstance->STATUS->setValue('CANCELLED');
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->add($mutatedInstance);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		// attendee modifications get generated in order of Added, Removed, Existing
+		$this->assertCount(1, $messages);
+		$this->assertEquals('REQUEST', $messages[0]->method);
+		$this->assertEquals(1, $messages[0]->sequence);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertCount(2, $messages[0]->message->VEVENT);
+		$this->assertEquals('20240715T080000', $messages[0]->message->VEVENT[1]->{'RECURRENCE-ID'}->getValue());
+
+	}
 
+	/**
+	 * Tests user modifying recurring (instance) event by adding attendee
+	 */
+	public function testParseEventForOrganizerModifyInstanceAddAttendee(): void {
 		// construct calendar and generate event info for modified event with two attendees
-		$calendar = clone $this->vCalendar1a;
-		$previousEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
-		$calendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
-		$calendar->VEVENT->SEQUENCE->setValue(2);
-		$calendar->VEVENT->add('ATTENDEE', 'mailto:attendee2@testing.com', [
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalInstance = clone $originalCalendar->VEVENT;
+		$originalInstance->add('RECURRENCE-ID', '20240715T080000', ['TZID' => 'America/Toronto']);
+		$originalInstance->SEQUENCE->setValue(1);
+		$originalInstance->DTSTART->setValue('20240717T080000');
+		$originalInstance->DTEND->setValue('20240717T090000');
+		$originalCalendar->add($originalInstance);
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedInstance = clone $originalInstance;
+		$mutatedInstance->SEQUENCE->setValue(2);
+		$mutatedInstance->add('ATTENDEE', 'mailto:attendee2@testing.com', [
 			'CN' => 'Attendee Two',
 			'CUTYPE' => 'INDIVIDUAL',
 			'PARTSTAT' => 'NEEDS-ACTION',
 			'ROLE' => 'REQ-PARTICIPANT',
 			'RSVP' => 'TRUE'
 		]);
-		$currentEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->add($mutatedInstance);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
 		// test iTip generation
-		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$calendar, $currentEventInfo, $previousEventInfo]);
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		// attendee modifications get generated in order of Added, Removed, Existing
 		$this->assertCount(2, $messages);
 		$this->assertEquals('REQUEST', $messages[0]->method);
-		$this->assertEquals($calendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
-		$this->assertEquals($calendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertEquals(1, $messages[0]->sequence);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertCount(2, $messages[0]->message->VEVENT);
+		$this->assertEquals('20240715T080000', $messages[0]->message->VEVENT[1]->{'RECURRENCE-ID'}->getValue());
 		$this->assertEquals('REQUEST', $messages[1]->method);
-		$this->assertEquals($calendar->VEVENT->ORGANIZER->getValue(), $messages[1]->sender);
-		$this->assertEquals($calendar->VEVENT->ATTENDEE[1]->getValue(), $messages[1]->recipient);
+		$this->assertEquals(1, $messages[1]->sequence);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ORGANIZER->getValue(), $messages[1]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT[1]->ATTENDEE[1]->getValue(), $messages[1]->recipient);
+		$this->assertCount(1, $messages[1]->message->VEVENT);
+		$this->assertEquals('20240715T080000', $messages[1]->message->VEVENT->{'RECURRENCE-ID'}->getValue());
 
 	}
 
-	public function testParseEventForOrganizerOnRemoveAttendee(): void {
-
+	/**
+	 * Tests user modifying recurring (instance) event by removing attendee
+	 */
+	public function testParseEventForOrganizerModifyInstanceRemoveAttendee(): void {
 		// construct calendar and generate event info for modified event with two attendees
-		$calendar = clone $this->vCalendar1a;
-		$calendar->VEVENT->add('ATTENDEE', 'mailto:attendee2@testing.com', [
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalInstance = clone $originalCalendar->VEVENT;
+		$originalInstance->add('RECURRENCE-ID', '20240715T080000', ['TZID' => 'America/Toronto']);
+		$originalInstance->SEQUENCE->setValue(1);
+		$originalInstance->DTSTART->setValue('20240717T080000');
+		$originalInstance->DTEND->setValue('20240717T090000');
+		$originalInstance->add('ATTENDEE', 'mailto:attendee2@testing.com', [
 			'CN' => 'Attendee Two',
 			'CUTYPE' => 'INDIVIDUAL',
 			'PARTSTAT' => 'NEEDS-ACTION',
 			'ROLE' => 'REQ-PARTICIPANT',
 			'RSVP' => 'TRUE'
 		]);
-		$previousEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
-		$calendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
-		$calendar->VEVENT->SEQUENCE->setValue(2);
-		$calendar->VEVENT->remove('ATTENDEE');
-		$calendar->VEVENT->add('ATTENDEE', 'mailto:attendee1@testing.com', [
+		$originalCalendar->add($originalInstance);
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		$mutatedInstance = clone $originalInstance;
+		$mutatedInstance->SEQUENCE->setValue(2);
+		$mutatedInstance->remove('ATTENDEE');
+		$mutatedInstance->add('ATTENDEE', 'mailto:attendee1@testing.com', [
 			'CN' => 'Attendee One',
 			'CUTYPE' => 'INDIVIDUAL',
 			'PARTSTAT' => 'NEEDS-ACTION',
 			'ROLE' => 'REQ-PARTICIPANT',
 			'RSVP' => 'TRUE'
 		]);
-		$currentEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$calendar]);
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->add($mutatedInstance);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
 		// test iTip generation
-		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$calendar, $currentEventInfo, $previousEventInfo]);
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		// attendee modifications get generated in order of Added, Removed, Existing
 		$this->assertCount(2, $messages);
 		$this->assertEquals('REQUEST', $messages[0]->method);
-		$this->assertEquals($calendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
-		$this->assertEquals($calendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertEquals(1, $messages[0]->sequence);
+		$this->assertEquals($originalCalendar->VEVENT[1]->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($originalCalendar->VEVENT[1]->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		$this->assertCount(2, $messages[0]->message->VEVENT);
+		$this->assertEquals('20240715T080000', $messages[0]->message->VEVENT[1]->{'RECURRENCE-ID'}->getValue());
 		$this->assertEquals('CANCEL', $messages[1]->method);
-		$this->assertEquals($calendar->VEVENT->ORGANIZER->getValue(), $messages[1]->sender);
-		$this->assertEquals('mailto:attendee2@testing.com', $messages[1]->recipient);
+		$this->assertEquals(1, $messages[1]->sequence);
+		$this->assertEquals($originalCalendar->VEVENT[1]->ORGANIZER->getValue(), $messages[1]->sender);
+		$this->assertEquals($originalCalendar->VEVENT[1]->ATTENDEE[1]->getValue(), $messages[1]->recipient);
+		$this->assertCount(1, $messages[1]->message->VEVENT);
+		$this->assertEquals('20240715T080000', $messages[1]->message->VEVENT->{'RECURRENCE-ID'}->getValue());
+
+	}
 
+	/**
+	 * Tests user deleting master instance of recurring event
+	 */
+	public function testParseEventForOrganizerDeleteMasterInstance(): void {
+		// construct calendar with recurring event
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		// delete the master instance (convert to non-scheduling)
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedCalendar->VEVENT->remove('ORGANIZER');
+		$mutatedCalendar->VEVENT->remove('ATTENDEE');
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(1, $messages);
+		$this->assertEquals('CANCEL', $messages[0]->method);
+		$this->assertEquals(2, $messages[0]->sequence);
+		$this->assertEquals($originalCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($originalCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+	}
+
+	/**
+	 * Tests user adding EXDATE to master instance
+	 */
+	public function testParseEventForOrganizerAddExdate(): void {
+		// construct calendar with recurring event
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		// add EXDATE to exclude specific occurrences
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedCalendar->VEVENT->add('EXDATE', ['20240715T080000', '20240722T080000'], ['TZID' => 'America/Toronto']);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(1, $messages);
+		$this->assertEquals('REQUEST', $messages[0]->method);
+		$this->assertEquals(2, $messages[0]->sequence);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		// verify EXDATE is present in the message
+		$this->assertTrue(isset($messages[0]->message->VEVENT->EXDATE));
+		$exdates = $messages[0]->message->VEVENT->EXDATE->getParts();
+		$this->assertContains('20240715T080000', $exdates);
+		$this->assertContains('20240722T080000', $exdates);
+	}
+
+	/**
+	 * Tests user removing EXDATE from master instance
+	 */
+	public function testParseEventForOrganizerRemoveExdate(): void {
+		// construct calendar with recurring event that has EXDATE
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalCalendar->VEVENT->add('EXDATE', ['20240715T080000', '20240722T080000'], ['TZID' => 'America/Toronto']);
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		// remove EXDATE to restore excluded occurrences
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(1, $messages);
+		$this->assertEquals('REQUEST', $messages[0]->method);
+		$this->assertEquals(2, $messages[0]->sequence);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+		// verify EXDATE is not present in the message
+		$this->assertFalse(isset($messages[0]->message->VEVENT->EXDATE));
+	}
+
+	/**
+	 * Tests user converting recurring event to non-scheduling
+	 */
+	public function testParseEventForOrganizerConvertRecurringToNonScheduling(): void {
+		// construct calendar with recurring event
+		$originalCalendar = clone $this->vCalendar2a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		// remove ORGANIZER and ATTENDEE properties to convert to non-scheduling
+		$mutatedCalendar = clone $this->vCalendar2a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedCalendar->VEVENT->remove('ORGANIZER');
+		$mutatedCalendar->VEVENT->remove('ATTENDEE');
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(1, $messages);
+		$this->assertEquals('CANCEL', $messages[0]->method);
+		$this->assertEquals(2, $messages[0]->sequence);
+		$this->assertEquals($originalCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($originalCalendar->VEVENT->ATTENDEE[0]->getValue(), $messages[0]->recipient);
+	}
+
+	/**
+	 * Tests SCHEDULE-FORCE-SEND parameter handling
+	 */
+	public function testParseEventForOrganizerScheduleForceSend(): void {
+		// construct calendar with event
+		$originalCalendar = clone $this->vCalendar1a;
+		$originalEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$originalCalendar]);
+		// add SCHEDULE-FORCE-SEND parameter to ATTENDEE
+		$mutatedCalendar = clone $this->vCalendar1a;
+		$mutatedCalendar->VEVENT->{'LAST-MODIFIED'}->setValue('20240701T020000Z');
+		$mutatedCalendar->VEVENT->SEQUENCE->setValue(2);
+		$mutatedCalendar->VEVENT->ATTENDEE->add('SCHEDULE-FORCE-SEND', 'REQUEST');
+		$mutatedEventInfo = $this->invokePrivate($this->broker, 'parseEventInfo', [$mutatedCalendar]);
+		// test iTip generation
+		$messages = $this->invokePrivate($this->broker, 'parseEventForOrganizer', [$mutatedCalendar, $mutatedEventInfo, $originalEventInfo]);
+		$this->assertCount(1, $messages);
+		$this->assertEquals('REQUEST', $messages[0]->method);
+		$this->assertEquals(2, $messages[0]->sequence);
+		$this->assertEquals($mutatedCalendar->VEVENT->ORGANIZER->getValue(), $messages[0]->sender);
+		$this->assertEquals($mutatedCalendar->VEVENT->ATTENDEE->getValue(), $messages[0]->recipient);
+		// verify SCHEDULE-FORCE-SEND is removed from the message (sanitized)
+		$this->assertFalse(isset($messages[0]->message->VEVENT->ATTENDEE['SCHEDULE-FORCE-SEND']));
 	}
 
 }