Ballots don’t have signatures on them. In this country, we go to great lengths to ensure ballot secrecy — which means there is no way to link a ballot to an individual voter when it is passed through a machine.
Except, there is a way to find invalid votes. There are supposedly ballots with perfect ovals (impossible), the ink that can be sampled (test if from the same source), different paper (phony ballot printing), chain of custody issues (several unsigned blocks of votes), there are dozens of ways to check if the ballot itself is valid even without a signature.
I will say it again: This is not a COMPUTER issue ... it’s a BALLOT issue.
Your whole premise falls apart if they manufacture ballots after the fact to match the machines. Counting pieces of paper means nothing. USB drives are missing, stacks of ballots with no chain of custody, vote totals quicker than the machines can process them, machines acceptable to hacking, machines that skewed the vote count in earlier elections where they had to count receipts. Both ballots stuffing and machine problems exist. The cheaters were able to walk and chew gum at the same time.