Frankly, that just sounds like a fire code / building code issue. Are these "apartment buildings" legal for habitation, with actual legal separate apartments, and not some weird subdivision/subletting situation?

In every place I have ever lived, having a clearly marked addresses and door numbers for apartments is required by the fire code. If there's an emergency that requires a fire or ambulance response, smoke in the air, etc, then "Nth floor, door on the right" is not a good thing to be explaining over the phone.