I've noticed this where I work. Some people who've had similar childhoods to mine tend to stand out to me, I can usually guess and then find out later I've guessed right when I get to know them better.

I occasionally have lunch or coffee with them (one on one I mean) at work. It's kind of weird to be discussing the horrors from the past then walk back in to work and put on the happy normal mask again. It's nice to occasionally be able to drop the mask. One of my work friends, though, I have to make sure I keep the boundaries up and not spend too much time with her. She has BPD and spending too much time with her is not good for my mental health (however, in small doses, we're good for each other).