I had shared this family calendar and forgotten about it … until I used it again to enter several appointments. Unfortunately, one family member thought that was a mistake and they had to be deleted. Which let me scratch my head, how I could restore those calendar entries either on Mac OS or in iOS.
First, I remembered that the calendar affected was an iCloud calendar. Second, Google delivered the following KB article upon searching:
https://support.apple.com/en-us/HT205018
And yes! This worked flawlessly. I was able to fetch a backup from just after midnight (12:35 AM, at first got afraid that no backup was available, until I checked that 12:35 AM is right after midnight, here in Germany we would say 0:35 hrs … ) and restore the calendar content. That worked and I had all my appointments back. Easy, wasn’t it?
PS: If your lost entries were not from an iCloud calendar, then you might try this solution:
https://discussions.apple.com/thread/3851319