infinitezero already has given the correct answer. I just wanted to add something about apartment numbers, but it's too long for a comment, so I hope it's ok to post it as an answer (although it isn't really an answer to your question).
I can't speak for Germany because I live in Austria, but here in Austria we "believe" in apartment numbers too, and I am very convinced, that German people also do. But when a courier wants to bring you a parcel, he has to take the elevator to reach your floor, and there he needs to know which button to press. Or he walks up the stairs, and then he also needs to know the level where your apartment is. Otherwise he had to search in every floor for an apartment with your apartment number, and couries don't have the time for such searches. So, when he rings you at the intercom, he wants to know two things:
- Are you at home? (This will be answered automatically when you pick up)
- Which floor? (This is the only thing you have to say)
There are some buildings, where the floor number is included in the apartment number. This is standard in hotels. (Room 101 to 126 are in 1st floor, 201 to 226 in 2nd floor etc., which also means, that there are no rooms with numbers from 127 to 200.) In bigger residential buildings you can find the hotel system as just described, but smaller ones (with less than 50 or 100 apartments) most often only use consecutive numbers. And those consecutive numbers don't give a hint to the floor number. I am living now in an apartment that has the number 15 and is in the the 3rd floor. 2 years ago I lived in another building and I also had apartment 15 over there, but there it was in the 4th floor.
Here in Austria (but not in Germany, as I have learned) there is also an additional number in bigger residential buildings which is called "Stiege" ("stair" or "staircase") that you have to tell when the courier rings you. This is if the building has more than one staircases to reach different apartments. The house has just one house-number, but you need to know which staircase to take. (For details read this question, but it is in German.)