TRUPLE WEIGHT, UPU SURFACE LETTER RATE
QUADRUPLE (4X), FIRST-CLASS LETTER RATE
DOUBLE WEIGHT AIRMAIL RATE SOLO USAGE
PREXIES USED AS POSTAGE DUE
John, This cover shows is a prime argument against yours in our initial discussion. This is inter-company mail sent to a Large, well-known entity of the time. The mailing post office forwarded the cover by airmail and 6c postage due was collected at the Canton, MA. Postage Office at the time of mail pick-up; as the mail probably went to Large Corporate Mail Box. The Canton, Ma. Post Office would have never held the mail for postage and mailed a Form 3548 to Los Angeles, Ca.; they knew Plymouth Rubber Company, Inc., as a large corporate manufacturer.
Everyday, probably a secretary, went to the Canton, Ma. Post Office to pick-up the corporate mail. Notice there is no "P.O. Box" on the address line - reason- Plymouth may not have had a real physical "Box". At the time of mail pick-up the mail would contain a pile a separate (sometimes banded) stack of mail requiring signatures or payment of postage due. The Postage Due was paid at the point, at the window. A Temporary Window Clerk may not have been provided a Stamp Drawer stocked with Postage Due stamps. Thus, the Window Clerk used Prexies, in lieu of normal Postage Due stamps, to pay postage due fees.
Additionally, during the World War II and the Korean War you had two additional problems: 1.) severe periodic paper shortages, and 2.) BEP back-up due to the paper shortages and war demand requirements that impacted stamp production. Case in point: The BEP could not print the OVERRUN NATIONS ISSUE of 1943-1944 due to the excessive war printing demands of WWII and thus subcontracted stamp printing to The American Bank Note Company.
All of these reasons lead me to believe Dave Phillips' contention that Prexies were periodically used and/or substituted, as needed, as lower value Postage Dues. Common sense says if a Postal Clerk indicates Postage is Due and you pay for it, you expect something placed on the envelope to prove payment. The Clerk had to show the transaction as the sale of stamps at that time… and the Clerk probably didn't care what stamps they used if they didn't have (or have access to) low-value postage dues in a Stamp Drawer. To a clerk, payment of postage due is payment of postage due, in-spite of whatever the regulations in the DMM.
The way Dave expressed it to me the shortages were sporadic and short-lived appearing randomly at some post office; offices were never out of Dues long enough to raise an issue or red flags.