Hello ShannonM1,
Thank you! Your question prompted me to take another look at this and I now have a solution.
Some background info: AddressBook goes back many years, to at least 2010, and it was deprecated with El Capitan (masOS 10.11) and replaced with Contacts in Sierra (10.12).
As I looked at these events they all seemed to be birthday events that originated from contacts in the old Apple AddressBook app. My earlier statement that I have other events in this calendar that I didn't want to lose was incorrect. Turns out that I had two calendars of the same colour and I didn't realize that the other was also selected; so, that "problem" was an error on my part.
Some prior version of MacOS converted these AddressBook birthdays into a calendar each with their unique URL back to AddressBook. I have no idea when or how that happened.
Now that i know that these, and only these, unwanted events are all in the same calendar I deleted that calendar – problem solved.
It still puzzles me why the "Delete" function is not an option for these events. I hope that in the future Apple allows the user to delete any event in a calendar and delete repeating events into the past as well as the future.
Thanks again!