This is ... incomprehensible.
My Google Calendar shows two events for the same sequence of meetings (same time, same location, same duration, same guest list). Both set of events display my email address in the 'Created By' field - yet one allows me to edit the event, the other does not. The reminders received by guests show me as 'Creator' for the former set of events, and as 'Organiser' for the latter set of events.
The event is private, as is the calendar visible to me. One additional discrepancy is that one set of events shows the Calendar Name in plain text, and the other shows it in a 'select/option' field. The event I created is private, and was created from within Google Calendar; no idea about the other one which is identical in every other respect bar what is evinced.
This came to my attention after the guests on the meetings list (whom I have no memory of including in the events in the first place!) complained about time-zone issues.
Anyway - why would an event I apparently created restrict my attempts to edit it?