Olivier presented an excellent case showing that a RECCURRENCE-ID's
primary role is that of an 'identifier'; and not a 'date/time' value that can
be relied on as the 'effective start' for a recurrence instance. This is made
even more clear in the following from 2445:
Section 126.96.36.199 Recurrence ID
. . .
The date/time value (RECURRENCE-ID) is set to the time when the original recurrence
instance would occur; meaning that if the intent is to change a
Friday meeting to Thursday, the date/time (RECURRENCE-ID) is still set to the
original Friday meeting.
With RECURRENCE-ID consigned to the role of an identifier
it clearly falls to DTSTART to represent a recurrence instance's
effective start time.
> For a recurring instance the effective start of an instance
> is defined in 2445 to be the RECURRENCE-ID.
That is not quite correct. The effective start of an instance
is its DTSTART. RECURRENCE-ID gets DTSTART as its
188.8.131.52 Recurrence ID
. . . The property
value is the effective value of the "DTSTART" property of the
This statement makes it clear that a recurrence instance has a
DTSTART property containing the "effective" value ... and this is
where RECURRENCE-ID gets its initial value. Initially, DTSTART
and RECURRENCE-ID have the same value. If the instance is
changed to a different time, DTSTART changes and
RECURRENCE-ID does not.