I don't know how the crap I get on these lists, I'm careful with who I give my # to and it pisses me off when they don't have the ability to call back and unsubscribe like they're supposed to.
It is not uncommon for these telemaggoters to use computers that dial numbers at random. As for a source of info, I would consider any business or organization that may have a connection to. Sometimes their privacy policy gives them the right to share information with third parties. A prime example is AARP.
Robo called 12 times in rapid succession but my clocking app hung up on them within a second, each time. They've called dozens of times before over months. That's why they've been permanently blocked and auto-hung-up on.