If this was used as the chief form of fraud, wouldn’t a simple recount reveal it? That is, as long as the ballots (or at least most of them) are paper. A recount simply would not support the altered count generated by the Hammer/Scorecard system.
What’s the chance the Dems implemented widespread fraudulent voting because they knew it would be detected? In other words, with no chance of winning, they could get more violence out of an overturned election result than just Trump winning outright?