Oh oh! I think they WERE being overwritten by an import from Google Calendar. I just saw this setting and had the first option selected:
Event Update Authority
Overwrite my event with any changes from the original source.
Do not re-import events. Changes made locally will be preserved.
Import events but preserve local changes to event fields.
I’ll try the other two and see how that goes and which I prefer. Thank you for now. I’ll close the ticket if I get it figured out.