ICAL in google calendar has extra event - outlook

Question

I'm facing issue wherein google calendar is showing extra calendar event.
ICS
PRODID:-//TEST//NONSGML Version 1//EN
VERSION:2.0
METHOD:REQUEST
BEGIN:VTIMEZONE
TZID:Asia/Kolkata
BEGIN:DAYLIGHT
DTSTART:19411001T000000
TZOFFSETFROM:+055320
TZOFFSETTO:+0630
RDATE:19411001T000000
END:DAYLIGHT
BEGIN:DAYLIGHT
DTSTART:18800101T000000
TZOFFSETFROM:+055328
TZOFFSETTO:+055320
RDATE:18800101T000000
END:DAYLIGHT
BEGIN:DAYLIGHT
DTSTART:19420901T000000
TZOFFSETFROM:+0530
TZOFFSETTO:+0630
RDATE:19420901T000000
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:19420515T000000
TZOFFSETFROM:+0630
TZOFFSETTO:+0530
RDATE:19420515T000000
RDATE:19451015T000000
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTAMP:19700119T063633Z
ORGANIZER:mailto:invite#a.com
UID:3fDJ2_gx5QJr4ygb#EqPBCMSzkxGfKg0
SEQUENCE:0
RRULE:FREQ=WEEKLY;WKST=SU;INTERVAL=1;BYDAY=SU,FR,SA
ATTENDEE;ROLE=REQ-PARTICIPANT;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION;RSVP=TRUE:mailto:a#gmail.com
ATTENDEE;ROLE=REQ-PARTICIPANT;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION;RSVP=TRUE:mailto:a#b.com
DTSTART;TZID=Asia/Kolkata:20200114T150000
DTEND;TZID=Asia/Kolkata:20200114T160000
SUMMARY:DEV TEST
TRANSP:OPAQUE
CREATED:20200114T091621Z
LAST-MODIFIED:20200114T091621Z
STATUS:CONFIRMED
LOCATION:Location
DESCRIPTION:Description
END:VEVENT
END:VCALENDAR
Calendar is created on wednesday for never ending weekly recurrence on days Friday, Saturday and Sunday. In google calendar I'm observing that there is an extra event created for wednesday(created date) including the recurrence events. I'm not observing this issue in outlook calendar.
Any idea why there is an extra event for the event create date created only in google calendar and not observed in outlook calendar.

Answer 1

I think this is due to different interpretations of the iCalendar specification:
https://www.rfc-editor.org/rfc/rfc5545#section-3.8.5.3
Particularly this section:
The "DTSTART" property defines the first instance in the recurrence
set. The "DTSTART" property value SHOULD be synchronized with the
recurrence rule, if specified. The recurrence set generated with a
"DTSTART" property value not synchronized with the recurrence rule is
undefined.
So the RFC doesn't define what happens when the DTSTART doesn't match the recurrence rule, and likely Google and Microsoft took different approaches.
To avoid this ensure your DTSTART occurs on a Friday, Saturday or Sunday.