Thanks for that, Joe. Unfortunately, the anniversary was not added to Calendar by following your procedure. I still had to put under Birthday.
Oops, I use Fantastical and in Fantastical > Settings > Calendars > My Calendar set > Reminders > Contacts there is an option for anniversaries. Unfortunately that is not true in Calendar.
If we knew what it was we were doing, it wouldn't be called research, would it?