In another thread, regarding the question of how much counterfeit money it would need to seriously impact a country’s economy, this site was cited about a German project during WWII to flood Britain with counterfeit pound notes.
This seems to imply that there’s some complex - and secret - mathematical scheme about banknote serial numbers. I always thought that those numbers were exactly that - serial, in the sense that they’re numbered sequentially: 9 483 287 is followed by 9 483 288, then 289, and that’s all there is to it. But maybe some central banks put more into it than that.
I understand that if there actually is some deeper meaning, the central banks might not be too eager to pass information about it to the public; but surely there’s information available about discontinued numbering schemes, if there have ever been sophisticated codes.
Kinda off topic here, but why exactly would one have to crack the code. It seems like you could just make up your own numbers. They could even all be the same number for small scale counterfeit. For larger scale, soon there would be a warning going out to retail stores not to accept money with that number, so you would just make bills with, say, one or two hundred different numbers. No one is going to try to match every bill they receive to a list of 200 seriel numbers. I guess this comes back to the U.S. coming out with new bills to thwart counterfieters. Whenever they come out with new bills and a customer says something like “Oh did ya see the new $20 bill. They say it’s harder to couterfeit” I like to respond with “Well, I just keep making the old ones then.” As long as their not making the old ones unusable, what point is there in making new ones. What counterfeiter is going to try to engrave new plates, when he can still pass off bills made with the old plates. Back to my digression, why bother cracking the code, just make up some numbers and use them. As for the OP, I have no idea if they use a secret code.
Older bills will come under more scrutiny though- so it will be tougher to use anything but perfect old bills. I would guess that most of the time counterfeiters aim for ‘good enough’ not perfect.
I wouldn’t know about the dollars, but I’ve been told by someone working at the french national bank that the serial numbers on former french bills indeed weren’t serial numbers, but created according to some algorithm that allowed to determine whether a given number would exist or not (actually, besides the serial number, there was another short numbers/ letters code on another part of the bill and one could be deduced from the other or somesuch).
I’m not sure what would be the purpose exactly, since people wouldn’t be able to tell apart a real from a fake bill by the serial number, anyway. Maybe in case the forged notes would be so perfect that only their normally unexisting serial numbers could allow to identify them? Or on a second thought possibly to allow machines to sort out the real and the forged bills automatically by reading the numbers when they are sent back to the central bank?
Slightly OT, but when I worked in my last job we had a very interesting moment with some African customers who weren’t happy with the change they received. It was all the right amount. It was the numbers on the notes they weren’t happy with. Apparently, they weren’t particularly lucky. They wanted to sort through the till to find some with luckier numbers on. We declined their offer.