All addresses will need to be clearly identified for mailing, and package delivery. With private. shippers, they might reverse the address and apartment number because why not? However, all addresses are still needed to be clearly marked. An example for John Doe at apartment 1 (manager’s apartment) will have the following address:
John Doe
APT 11
5405 Kent Way
Pittsburgh PA 15201
Many people place the street address in the second line, but to me, it makes most sense to place the apartment on the second line. Any mail sent to you will be in this format. The front apartment will end in 1, and the back apartment will end in 3.