2.1.1.

There are interoperability problems when the sender is attempting to reschedule an entire event, but does not send recurrence properties and does not wish to replace the recipients set with the new set. The sender is trying to simply move the set from one time to another (1pm to 2pm), adjust duration, etc. A simple example would be a recurring meeting that is currently from 1pm to 2pm, that is being rescheduled to 4pm to 5pm, for all instances. Implementers might not want to lose the recipient’s changes, personal notes, and updates to the set by replacing their set with what’s received.