So I got an event in notification center from 2014 that wouldn't go away. I've deleted it from the calendar, I've restarted, I've turned iCloud calendar sync off and on - nothing.
You might have a phantom calendar still residing on the Mac. Do a Spotlight on the event name and see if something comes up. If so, do a "Show In Finder" and you can delete the event(s).
You might have a phantom calendar still residing on the Mac. Do a Spotlight on the event name and see if something comes up. If so, do a "Show In Finder" and you can delete the event(s).