It will be even better if you give a date/month for their latest post to be accepted them for the votes.
I addressed that part
here. So by active users we understand users which were and / or are active during current year (and, of course, made notable contributions during this year).
How do you define active user? Only by "Last Active: " column on profile page?
I will suggest last post the made.
For example last post made before November 2021, receive any vote, will not be counted. Also after the launch of the award pool if the same criteria of the user makes any post then that will not include them as whitelisted too. I think this will prevent them to abuse the rule.