Cross check system is to prevent people from voting in more than one state. Most people that move from one state to the next don’t run down to the voting registration office to remove themselves. They move, go to the next state and register there sometime prior to an election. That doesn’t mean they are trying to vote in both states, but there are obvious cases where people have double voted. In 2012, North Carolina found 35,000 people had possibly voted in NC and another state during that election cycle. Some of those people had exact name match, birthdate and last four of their SSN. Since there was no further investigation into the matter it was left as a possibility of 35,000 double voting citizens. Most people that vote more than once seem to be caught because they publicly boast about it such as the Ohio poll worker that bragged about voting for Obama six times in 2012. There was a woman that was caught voting twice for Trump in Iowa in 2016. Both were caught due to social media posts and people turned them in. Voter fraud, real, imagined or whatever will always be an issue if it is not thoroughly investigated by each state verifying their voting rolls, then each cross checking their rolls against the 49 other states. A person can easily vote in person in one state and absentee ballot vote in another state if they have two addresses. How often that happens is debatable, but saying it never happens is ludicrous. There have also been more than 40 cases of voter fraud since 2000. There were 17 counts of voter fraud against a single man in Virginia for trying to register 17 dead people. He was only caught due to the registrar personally knowing one of the dead people the guy tried to register.