It wasn’t really *massive* cheating. It was a few thousand votes in about a dozen counties in three or four states. However,the *consequences* were certainly massive.
We will never know the extent because the records were destroyed by corrupt officials.
After 2020, I learned that, historically, the Census Bureau polled and predicted the total votes for president, going back many US election cycles.
This estimate was not predicting for whom votes would be cast but simply how many would vote for president.
Their track record for the total number of votes was amazingly close - until the 2020 presidential election, where some 4.5 million or so votes were counted over the Census Bureau estimate.