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iCalendar Recurrence Problems and Recommendations
6. Best Practices

6.3.

Reschedules occur in two different varieties (iTIP), rescheduling where the RECURRENCE-ID is supposed to be changed and when RECURRENCE-ID is not supposed to change.

6.3.1.Clause6.3.1Rescheduling of one or more instances where RECURRENCE-ID is not subject to change. In this case, recurrence properties are not sent, so the receiver is expected to keep the current recurrence set and simply reschedule what’s already on the calendar to different dates/times.
6.3.2.Clause6.3.2Rescheduling of the entire set, where RECURRENCE-ID is expected to change. In this case, recurrence properties are sent, so that the receiver is expected to replace the existing recurrence set with the incoming set.
6.3.3.Clause6.3.3Why not always update RECURRENCE-ID? Since RECURRENCE-ID