From my own experience in business, I have seen numerous examples of financial instruments such as cheques, money orders, traveller's cheques and bank transfers that have NOT been endorsed or stamped by a bank despite the fact that they have been banked and the funds have been deposited into my account.
In fact, it you think about it (and idiots like Sandy Larsen obviously have not) is easy to understand why that might be. Why are money orders endorsed with a bank stamp in the first place? The answer is, that it is a confirmation that the person who is presenting the money order, is the person to whom the money order is addressed, i.e. the payee. When a person presents a money order for cashing (at a bank or a post office) or for banking into their own bank account (at a bank), they present the money order to a teller. The teller will ask the person for some form of identification (driver's licence, ID card) to show that they are the payee. When the teller is satisfied with their identification, they will stamp the money order, and that acts as an endorsement.
However, when a company or business is presenting the money order, it is likely to be just one among many being banked at the same time. Klein's Sporting Goods was a very big company that had been around since before WWII, and they didn't just sell guns. they dealt in sports equipment across the whole range of sports, leisure and pastimes; racquet & bat sports, ball sports, golfing equipment, fishing tackle, sports and hunting apparel, even musical instruments! They were a business that advertised in dozens of magazines and newspapers across the whole of the USA. A business that large is going to be banking hundreds of cheques, money orders, and charge card slips (as well as a large amount of cash) every day. They would have used a courier, or an armoured car service (or perhaps an employee) to deliver their cash and document bags to the bank for banking. Did the courier driver or the driver of the armoured car or his shotgun, have to wait while the teller individually hand-stamped hundreds of money orders and cheques? Of course not, and why? Because these financial instruments were already endorsed by the payee, and this was indicated by their stamp on the back of the instrument, in this case....
PAY TO THE ORDER OF
THE FIRST NATIONAL BANK OF CHICAGO
59-91144
KLEIN'S SPORTING GOODS, INC.
... was all the endorsement that the bank (and ultimately, the Fed) needed to verify the identity of the payee. The reference number will be either an authorisation number for Klein's, or the last seven digits of their bank account number at that bank (my endorsement stamp had the last seven digits of my account number at the branch where I bank (plus a two-digit suffix to indicate which sub-account it is to be banked into)
I can therefore reasonably conclude that the Klien's endorsement stamp is sufficient proof that the money order was indeed processed.