I’ve noticed when rolling that if I start a community with three character models, then put them in the pool, or keep playing, or delete them, then I won’t see them come up when rolling next time. Or I get the same faces as the ones I just rolled, but they’re wearing different outfits. BUT…if you wait a day or two before rolling again then that all goes out the window. They’re just as likely to come up again no matter where their doppelgängers are.

I don’t say this to contradict you, but only to add data to us all trying to figure it out. I’m curious too and want to unlock the secrets of rolling for “perfect” survivors.