The secret ballot is so important that we tolerate the very possibility that our votes are counted differently than we intended. Think about it; if not for secret ballot considerations, you could cast your vote and see it instantly added to your candidate’s total at your precinct. But, precisely because of that, everyone else would know who you voted for.Likewise in the case of someone who is found to have voted illegally - you know who did it, and in your heart you know who they voted for - but that is not provable. Because, secret ballot.
If they voted absentee, they had to submit a paper ballot. I think that was the case in Colorado. With a paper ballot, why wouldn’t they be able to find out who got the votes?
Ballots cast, not just registrations. Am I missing something?