Earlier quoted context omitted.
Robocalls I get typically assign a caller ID of my area code (and sometimes prefix) with random other digits. Most 408-73x prefixes were originally specific to Sunnyvale CA and are therefore easy to distinguish.
Yeah but I'm not sure they're genuinely random. If you try Googling them you see that they're generally listed as robocallers. Whereas if you Google people you know, I don't think you'll see them being listed as robocallers (at least it hasn't been the case when I've tried). That suggests they don't just randomly pick numbers.
I just did a quick check of the last 10 or so I received. None of them were listed as robocallers. They were all legit phone numbers of innocent people who live in my area.