Detroit Michigan
Main Post Office was created in 1934.
yes
Main Post office (Head Post Office) to Main Post Office (Head Post Office)
Buffalo Main Post Office was created in 1911.
Evanston Main Post Office was created in 1905.
Thermopolis Main Post Office was created in 1933.
Old Chicago Main Post Office was created in 1921.
Detroit 73 miles assuming that is the type of thing you are seeing and thereby asking about, it means that from that sign to the Detroit city limit on this route is 73 miles. same for the post office, from that sign to the post office on this route.
1510, going from the main post office in Denver to the main post office in Toronto.
U.S. Post Office-Port Townsend Main was created in 1893.
US Post Office-Santa Barbara Main was created in 1937.