Could be change of address form. It only lasts a year so sometimes people do it for several years.

I doubt anybody would be so brazen as voting dozens of times in their own name. The cheating they just assign each ballot to a different non-voter.

But it's great to be hyper-vigilant even if it makes Trumpers look like conspiracy theorists. The more the cheaters think people are watching the less comfortable they'll be cheating.