Dear John, thanks again for your observations and comment.
I've searched the web archive of the Journal of Aeronautical Sciences, and have found this page from January 1949 issue, mentioning on the addresses for correspondences (red frames added by myself);


It says that all correspondences regarding manuscript publication etc should be addressed to the Editorial Office of the Journal, which is located in 2 East 64th Street, New York 21, New York.
However, this cover was incorrectly addressed to the "Editor" at 20th & Northhampton Street, Easton, PA., where the Publication office of the Journal, which was only responsible for correspondences for journal subscription, was located.

Thus this cover, received at the Publication office, has been forwarded to the Editorial Office in NY.
My thought is that this mistake (e.g. sending the correspondences aimed to Editorial Office to Publication Office, or vice versa) had been so frequently occurring that the Institute of the Aeronautical Society, who was the publisher of the Journal, have had a specific contract between the public messenger to handle the transfer of misaddressed correspondences between the two Offices.
Hironobu
- Nov 10: edited for clarity