Tl;dr: There's a lot of garbage in the database, but it doesn't matter because a) no one trusts the data, b) no one's falsely getting the money. So they haven't

Tl;dr: There's a lot of garbage in the database, but it doesn't matter because a) no one trusts the data, b) no one's falsely getting the money. So they haven't done anything about it because cleaning up millions of PII records was too expensive. No one who has dealt with databases would be surprised that a database older than most people alive would be full of garbage.