This reminds me of a book I read recently about the history of paper. It talked about how the profession of “Rag Man” was a real thing as these guys sold their collected rags to paper mills for recycling into new paper. Before this I had thought the term simply meant someone who was so poor that they were ragged.
Update: some googling shows me that the Boggs Tubman note is something different, so it goes back to the Youtuber being the idiot. Boggs was still just a fraud.
Sounds like your rule won’t do anything, then. If it doesn’t happen now, when it’s allowed, then doing nothing to change that will result in nothing changing.
Based on your characterization of cashiers’ behavior, though, it sounds like this isn’t actually a problem with a solution that makes sense. If retailers are so universally unconcerned by the threat of counterfeit old money, I’m fine with following their lead.