My understanding with debt collectors, is that they usually purchase a spreadsheet with very limited data, and there is almost never a paper trail for said debt. Which also means debt has a habit of showing up on multiple spreadsheets that keep getting resold. I think planet money did a podcast on this topic.

Patio11 also wrote about talking to debt collectors with regards to identity theft. https://www.kalzumeus.com/2017/09/09/identity-theft-credit-r...