I must admit, I looked at that document online for a long time but didnt catch the sequential PO box. To repeat what I have said on other threads: amateurs did this. Actually there are thousands of amateurs who would have done a better job. At least they would have used a realistic PO Box or even a real address at an ANG base.
I'm sure you know how easy it would be to pick up an old typewriter at a flea market, garage sale or estate sale. How could they be so dense? Or did they think no-one would notice?