Tell me how much harder and less reliable it is to track billions of individual serialized objects over time vs. a database transaction.

I always just assumed that somewhere in the banknotes lifecycle those serial numbers are all getting written into a database… I kind of assumed that based on examples where the government was able to trace where large amounts of cash had come from and what it got spent on when doing major crime investigations or things like DB Cooper and how confidently they proclaim that none of the cash (that wasn’t “lost” and then found by various searches or the public over the years) was ever spent. I assumed it was probably part of obligatory regulations to do with money laundering or something equivalent and thus they all had to do it.