They know a lot more than you think they would, that is for sure!
When I was getting a security clearance in basic training in the 1980's, people were contacted and asked about me who's names I couldn't even
remember. I thought it was bizarre that people like my first grade teacher, youth group leader, summer camp counselors, etc. were sent questionnaires
asking all sorts of things about me. I couldn't even tell you the name of any of those people, but the government sure knew who they were
I had no idea until my mom told me she had been getting some "strange" phone calls from people she hadn't seen in years asking if I had gotten in
trouble with the law or something. It was very spooky...
I ended up not taking the crypto job, but I was very glad that I hadn't done anything that could have been embarrasing or illegal, lol.