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Print at Jan 20, 2026, 11:01:00 AM

Posted by support at Jan 1, 2018, 4:54:18 PM

Re: After a date shift, the appointment appears twice
Thanks,

We're aware of the specs you mention, but as I noted in my last post, what the specs say and how others have chosen to implement it are two separate items wink

Since we are not internally ical-based, we rely on 3rd party libraries to help where we integrate with iCal feeds. And at this time, the handling of RECURRENCE-ID is slim to none.

Just two of many public threads where people are wrangling with this issue (this time from a Wordpress calendar provider) https://icalevents.com/4437-correct-handling-of-uid-recurrence-id-sequence/
also https://stackoverflow.com/questions/11456406/recurrence-id-in-icalendar-rfc-5545

IBM has this to say about the subject (I have added emphasis)

RECURRENCE-ID: This is a simple property, but is often misunderstood and is very important... particularly when updating a calendar entry.
RECURRENCE-ID refers to the ORIGINAL starting time for a single instance of a repeating meeting. If a meeting instance changes, its RECURRENCE-ID does NOT change... just its DTSTART and DTEND change.
It may be difficult to determine the RECURRENCE-IDs that represent instances identified in an RRULE. For the first instance, this is the DTSTART. IBM does not currently provide the ability to get a list of RECURRENCE-IDs in the initial release, but this can be done via interpretation of the RRULE.
Also, while a recurrence ID may specify a range (this and future), this is not currently supported by the API in any way. The reason for this is because other implementations (like Outlook) do not honor this and there are some ambiguities in the standard regarding the use of this. Our API only accepts or outputs single instance exceptions.

When localendar first started (in 1999!) iCal was a spec followed/used by basically no one. In the past 18 years (!!!) we have seen things mature to the point where it's a standard that works in about 95% of all cases. It's amazing the amount of interoperability and portability we have now compared to what we had back then. We'll continue to monitor the situation, and if everyone settles on a common implementation for RECCURENCE-ID, then we'll support it, too.
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Marc Higgins
Support Associate, localendar.com
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