I'm not sure why the P.O. Box issue is still being talked about. It was on the official letterhead for the Fighter Group on one of the real documents from Bush's file, and on a letter from Bush to Killian.
But the fact these memos are not on letterhead--now that's a real indicator of forgery. No other documents in the files are like that.
Don't be focused on the one legitimate part of this. There are too many illegitimate aspects of these memos that must be hammered away on repeatedly.
The best indicator of forgery is the fact that documents were produced using M.S. Word. (they appear exactly like they were typed on the default settings of M.S. Word--which is extremely hard to duplicate on a type writer from 1973, and impossible to duplicate in 1973 because one would not have an example to try and duplicate).