Here's another piece about how postage stamps were used by mail order firms (such as Sears and Montgomery Ward):
Quote:
"The heaviest usage of dated [precancels] was from July 1938 through the World War II years. The large mail order companies (Montgomery Ward and Sears) used them on into the 1960s.
Another note is that payment for orders was commonly made with postage stamps. These stamps were sent to the mail room, precanceled, and used on the outgoing mail. This practice lead to a wide variety of stamp issues precanceled."