I think it is just a case of the words "one punch" or "a punch" etc. as used in the books. Anyway, this has become very interesting...Off the original subject. I never bothered to find out exactly how a mint mark punch is made. I've called several modern letter punch sellers today and guess what - everything they sell is imported! They could not answer my questions. So far, without any corroboration, this is what I believe: A long, square steel "shank" is rounded at one end and annealed. Then a hub with the engraved mint mark is pressed into it. Possible several times between annealing? This operation was probably done at the twentieth century mint in the same way as they did to make all the letter and star punches used to make Large cent dies in the nineteenth century. I shall find out about this too.
Well, I also know admittedly nothing about this, but there's a hole in your theory. The rod, when pressed into the hub, would have a mint mark pressed into it's surface. A die would leave the type of mark that you seek. That said, I do know that until the very recent past mint marks were added to working dies, not the hubs. Currently, the hubs are pressed with a complete date and mint mark.
And FWIW, the Mint probably would have the manpower, the facilities, AND the materials to make a mint mark punch. They're metal workers at the end of the day.
Actually, I have just learned that the punches for the devices were usually made outside the mint! I'm getting a phone call later in the week to confirm that. I'm glad you started me on this "trip" of discovery!
Well, just an outside, uneducated, ignorante observation. Backup. Don't we always employ backup in everything we do? (wise ones do) Redundancy.......So why not a few extra 'punches'?
Like everything the government uses or buys, there is a law that it has to be specially made so it costs 100 time what it should.