> Banks don't know who gets what serial number when you withdraw cash.
Do you have evidence to back this up?
In Canada, many bank branches don't carry cash except at ATMs, which means 100% of the cash transactions at those branches go through ATMs. Bills are inserted without an envelope, and are counted one by one, which means they're already being optically scanned (read: photographed) to determine the denomination. It's not a stretch that the serial number could be captured at this phase. When bills are withdrawn, they're withdrawn off the top (or bottom) of a stack of bills, so it is known which elements are removed from the stack. Again, it would not be infeasible to track all of the serial numbers in the stack, in order, and associate those numbers with withdrawals.
I do not have evidence that this occurs, but I've always assumed it was at least possible. It's technically trivial. But if you're claiming that it's either impossible or it doesn't happen, I'd need some convincing evidence that that's the case.
according to a german report ATMs can scan the serial numbers when the money is dispensed, logging them to the account from which the money is withdrawn. it's generally not done now, but it is technically possible. in china it apparently is already enforced. elsewhere at a minimum they track which notes are sent to which ATM in order to resolve ATM robberies. likewise when money is deposited, it is being scanned for fakes. counting and sorting machines can track the serial number too:
