»When a calendar component is created, its sequence number is 0. It is monotonically incremented by the “Organizer’s” CUA each time the “Organizer” makes a significant revision to the
The “Organizer” includes this property in an iCalendar object that it sends to an “Attendee” to specify the current version of the calendar component.
The “Attendee” includes this property in an iCalendar object that it sends to the “Organizer” to specify the version of the calendar component to which the “Attendee” is referring.
A change to the sequence number is not the mechanism that an “Organizer” uses to request a response from the “Attendees”. The “RSVP” parameter on the “ATTENDEE” property is used by the “Organizer” to indicate that a response from the “Attendees” is requested.
Recurrence instances of a recurring component MAY have different sequence numbers.«
So this means that we have tocheck whether we are organizer or attendee (IS_ORGANIZER), increase the SEQUENCE number only if we’re organizer (at which time – after receiving or before sending?), handle recurrence instances correctly.