[He has a list of people when they arrive whether he talks to them or not. If they address everyone he listens to what he can and takes notes. Totally not creepy. But departure dates are trickier unless a friend or roommate of theirs lets everyone know.]
You can always ask the wardens about someone, but it's not that strange to not see them for a day or two and then it's more than a few days and you just start to assume.