welfare lists

Likely, they're real people. It's no secret there was a HUGE enthusiasm gap. Democrats were so unpopular they often chose not even to campaign. If you're a standard low-info, low-interest voter, you care a lot more about what's on Netflix or where the weed is than who's running for State legislature or what Proposition [number] is. Right?

But, there are extensive registry campaigns. Historically, Dems have done massive voter registration drives especially during presidential election years. Most states have motor voter laws that automatically register people when they get or renew their driver's license, etc. This means we have mass voter registries. Our disinterested voters are certainly registered, even if they don't give a crap and wouldn't vote. They may even be registered in multiple locations if they've moved and the county clerks do a poor job of cleaning those registries.

Again, the people are real.

Dems know that these people are real and that they likely won't show up to vote. They know where they are because they have overwhelming access to the local election machinery. So, they take this massive pool of potential votes which almost certainly won't turn out, break them down by demographics so they can target the ones they're likely not to show, and then post completely valid mail-in ballots in their name knowing that no one will ever check because the names are legit.

Getting caught looks like Michigan. People showed up to vote and were told they had already voted absentee. They're allowed to fill out provisional ballots, but that doesn't matter. Either they don't count the provisionals at all if the race isn't close enough, or if they do, the provisional only zeroes out the fake ballot already cast in their name. There's very little disincentive to do this.