the PO box showed up in actual documents...your beating a dead horse
As a result references to today's structures has little relevance to those in place back in "W"'s time.
Another item of note is that Post Office Caller Service, which also uses a POBox number address format, was non-existent until 1975 when I pushed it to implementation with a major rewrite of USPS rules.
Many places adopted an ad hoc "Phantom Box" service. It was essentially "will call" service, but with a PO Box number address. No box was used. There were, of course, variations. Pittsburgh PA had about 15,000 physical boxes tied up to give "phantom box" numbers to major banks and businesses.
I straightend out all that nonsense in 1975.
Almost got fired for it too since the last thing a federal bureaucrat is allowed to do is correct a problem!