First playthrough, I missed two survivors. I didn't get the achievement for having collected all survivor combo cards.
On the second playthrough (having restarted my first playthrough), I just got through saving both of the survivors I missed the first time. Neither of them gave a combo card, though. So I'm still lacking that achievement.
In order to narrow down just what's going wrong here, I think I need a list. For now, here are the cards I'm missing, most (all?) of which are not survivor cards, though I don't know which are, if any: