It happens often. A person goes to the polling place and is told, "You've already voted. You can't vote again." That person's vote has been stolen.
It happens especially in precincts with a large transient population, and when the voter goes to the polling place late in the day.
Precincts with large transient populations: large cities and college towns. Why is it that those are almost the only places where Democrats win?
In precincts with large transient populations, the fraudsters assume that if a name on the voting roll has not voted by, say, six o’clock, it’s because that person no longer lives there. If they cast that person’s vote, it’s not likely that the person will show up and make a stink. And if it’s a Democrat dominated precinct, even if a late voter does show up, there will not be much that he or she can do.