add a past event to iCal

I have checked, re-checked, triple checked setting in Calendar so that it shows Syncs ALL EVENTS.

I want to add an event that occurred Dec 9, 2016 to keep a record of it. I have tried entering and adding it multiple times but it will not add it! Yet there are other innocuous events that occurred at or near that date that are showing up and I could give a flip if they are still there. WHY CANNOT I ADD A PAST EVENT????????