I was considering something similar, only making a single annual checkbox property that contains every event we have that year. 2022 Events: Annual Meeting, Security Conference, etc.
Then you can just duplicate 1 field every year and import registration csv files and tag people with the event they attended. You can also update the property with a new event if something comes up that you hadn’t planned on. Not very elegant, but seems like it will work and keep the number of custom properties needed to track to a minimum.
This may turn into a data problem, but for now, I’ll try it and see if it works well enough.