How exactly is a late postmark relevant to identification here? I often get eBay
purchases mailed to me bearing stamps that are older than I am. Okay, those are generally mailed by stamp dealers who are getting rid of stock that they'd have to sell for less than face, but who's to say that someone in 1930 didn't use some stamps that had been forgotten in a book, box, or drawer for several years?
Granted, a later postmark will more likely
appear on a later issue, but unless a stamp has been declared invalid, there's nothing preventing
it from being used at a late date. So even though the late date suggests
that this stamp would probably be a 632, it's really only the 11×10½ perfs that would definitively identify it as such. (And yes, I do believe that it is a 632.)