Burton,
As you probably already know, this appears to have started out as a UC8 (AIR 6¢ MAIL in rectangular box on 2¢ PSE) and somehow or other it was also overprinted with the 1946 REVALUED | 5¢ | P.O. DEPT. surcharge which was normally used only on the 6¢ orange PSE of 1942-44. This is certainly possible if some remainder of the UC8 was overprinted.
HOWEVER, I would be suspicious unless you have provenance which goes back to the time the items appeared in the post offices. Since the time when sophisticated digital software and printers have been available, it would be relatively easy to overprint the 5¢ REVALUED surcharge on a legitimate UC8 envelope. I think I could do it by copying the overprint from the catalog and adjusting it for proper size and then adjust my laser printer to place it in the right place over a UC8. I could do even better by scanning a UC10 and removing the orange leaving only the black overprint and then repeating the calibration and location.
I am somehwat surprised that such an error has not previously been noted and added to the catalog. Because it is so easy to create and print in a laser printer, I would not expect anything until it had been expertised. OTOH, someone may already know that such an error has been uncovered and already expertised.
jimbo
just my ½¢
