In the condo lobby, there are two elevators, facing each other across the lobby. However there has never been any sign of this second elevator in the hallway outside Frasier's condo - in fact, it would be where Frasier's living room is if there were a second one.
Correction: A possible explanation would be that the elevator on the right leads to the parking garage and basement, going no higher than the lobby and thus not interfering with the apartments above.
When Cam admits Frasier (Kelsey Grammer) to his apartment, we see on his door that he lives in 2001, as you would expect, given that he lives directly above Frasier who is in 1901. In Season 7's The Fight Before Christmas (1999), however, it is said that Cam lives in apartment 2000.