Thanks for your response!
Included are examples (from two CalDAV clients) of the event before adding and after adding an attendee.
Apple Calendar on macOS Catalina
Before
BEGIN:VCALENDAR
PRODID:-//Apple Inc.//Mac OS X 10.15.3//EN
VERSION:2.0
CALSCALE:GREGORIAN
BEGIN:VTIMEZONE
TZID:America/Toronto
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
DTSTART:20070311T020000
TZNAME:EDT
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
DTSTART:20071104T020000
TZNAME:EST
TZOFFSETTO:-0500
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
CREATED:20200227T145832Z
UID:5C7B31BA-459A-4F41-B9D2-96513D6280CB
DTEND;TZID=America/Toronto:20200227T113000
TRANSP:OPAQUE
X-APPLE-TRAVEL-ADVISORY-BEHAVIOR:AUTOMATIC
SUMMARY:Broken Event
LAST-MODIFIED:20200227T145841Z
DTSTAMP:20200227T145840Z
DTSTART;TZID=America/Toronto:20200227T110000
SEQUENCE:1
CLASS:PUBLIC
END:VEVENT
END:VCALENDAR
After
BEGIN:VCALENDAR
PRODID:-//Apple Inc.//Mac OS X 10.15.3//EN
VERSION:2.0
CALSCALE:GREGORIAN
BEGIN:VTIMEZONE
TZID:America/Toronto
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
DTSTART:20070311T020000
TZNAME:EDT
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
DTSTART:20071104T020000
TZNAME:EST
TZOFFSETTO:-0500
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
TRANSP:OPAQUE
DTEND;TZID=America/Toronto:20200227T113000
DTSTART;TZID=America/Toronto:20200227T110000
UID:5C7B31BA-459A-4F41-B9D2-96513D6280CB
DTSTAMP:20200227T145840Z
SEQUENCE:1
X-APPLE-TRAVEL-ADVISORY-BEHAVIOR:AUTOMATIC
SUMMARY:Broken Event
LAST-MODIFIED:20200227T145937Z
CREATED:20200227T145832Z
ATTENDEE;PARTSTAT=NEEDS-ACTION;CUTYPE=INDIVIDUAL;EMAIL=adrwxyz@gmail.com:ma
ilto:adrwxyz@gmail.com
ATTENDEE;ROLE=CHAIR;EMAIL=andrew@alexanders.xyz;PARTSTAT=ACCEPTED;CN=andrew
@alexanders.xyz;CUTYPE=INDIVIDUAL:mailto:andrew@alexanders.xyz
CLASS:PUBLIC
ORGANIZER;:mailto:(null)
END:VEVENT
END:VCALENDAR
Fantastical 3 on macOS Catalina
Before
BEGIN:VCALENDAR
PRODID:-//Flexibits Inc./Fantastical for Mac 3.0.5//EN
VERSION:2.0
CALSCALE:GREGORIAN
BEGIN:VTIMEZONE
TZID:America/Toronto
X-LIC-LOCATION:America/Toronto
BEGIN:DAYLIGHT
TZNAME:EDT
RRULE:FREQ=YEARLY;UNTIL=20060402T070000Z;BYMONTH=4;BYDAY=1SU
DTSTART:20000402T020000
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:DAYLIGHT
TZNAME:EDT
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
DTSTART:20070311T020000
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:STANDARD
TZNAME:EST
RRULE:FREQ=YEARLY;UNTIL=20061029T060000Z;BYMONTH=10;BYDAY=-1SU
DTSTART:20001029T020000
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
END:STANDARD
BEGIN:STANDARD
TZNAME:EST
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
DTSTART:20071104T020000
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTAMP:20200227T040640Z
UID:38D883D4-5899-415D-B9C6-D3E85566BA35
DTEND;TZID=America/Toronto:20200227T103000
TRANSP:OPAQUE
SUMMARY:Broken Event
CREATED:20200227T040640Z
DTSTART;TZID=America/Toronto:20200227T100000
SEQUENCE:0
X-APPLE-TRAVEL-ADVISORY-BEHAVIOR:AUTOMATIC
CLASS:PUBLIC
END:VEVENT
END:VCALENDAR
After
BEGIN:VCALENDAR
PRODID:-//Flexibits Inc./Fantastical for Mac 3.0.5//EN
VERSION:2.0
CALSCALE:GREGORIAN
BEGIN:VTIMEZONE
TZID:America/Toronto
X-LIC-LOCATION:America/Toronto
BEGIN:DAYLIGHT
TZNAME:EDT
RRULE:FREQ=YEARLY;UNTIL=20060402T070000Z;BYMONTH=4;BYDAY=1SU
DTSTART:20000402T020000
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:DAYLIGHT
TZNAME:EDT
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
DTSTART:20070311T020000
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:STANDARD
TZNAME:EST
RRULE:FREQ=YEARLY;UNTIL=20061029T060000Z;BYMONTH=10;BYDAY=-1SU
DTSTART:20001029T020000
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
END:STANDARD
BEGIN:STANDARD
TZNAME:EST
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
DTSTART:20071104T020000
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTAMP:20200227T145748Z
UID:38D883D4-5899-415D-B9C6-D3E85566BA35
DTEND;TZID=America/Toronto:20200227T103000
TRANSP:OPAQUE
SUMMARY:Broken Event
CREATED:20200227T040640Z
DTSTART;TZID=America/Toronto:20200227T100000
SEQUENCE:1
X-APPLE-TRAVEL-ADVISORY-BEHAVIOR:AUTOMATIC
LAST-MODIFIED:20200227T145748Z
ATTENDEE;PARTSTAT=ACCEPTED;CN=andrew@alexanders.xyz;CUTYPE=INDIVIDUAL:mailt
o:andrew@alexanders.xyz
ATTENDEE;PARTSTAT=NEEDS-ACTION;CUTYPE=INDIVIDUAL;EMAIL=adrwxyz@gmail.com:ma
ilto:adrwxyz@gmail.com
CLASS:PUBLIC
ORGANIZER;:mailto:(null)
END:VEVENT
END:VCALENDAR |