I've been an election official for more than 20 years and I believe you have been misinformed. First, polling locations are staffed with nearly a dozen randomly assigned elderly people. They are trained how to validate a photo ID, the voters address, obtain a signature and finally distribute a numbered ballot that has been signed by 2 witnesses. So, for your theory to work, a dozen or so people would have to conspire together produce extra live ballots. It's hard enough for two people to keep a secret, now your asking a dozen to keep quiet. Second, polling districts/wards are kept small to ensure an orderly voting process. I believe most locations are designed to have 2,500-3000 registered voters. I saw the largest one was in New Jersey and they had 6k. Now, to swing vote counts your asking multiple polling locations and dozens of workers to conspire. In the 5-7 swing states and/or swing counties, you asking hundreds or thousands of poll workers to conspire together in secrecy. I could also address ballot counts, ballot paper in weights, QR codes, bar codes and watermarks, but that seems like overkill. IMO, it's easier to counterfeit money than votes and ballots.