Then there's needing to contend with possible serial number scanning occurring at automated stations and at financial institutions, cataloging the movements of specific bills, detecting clones (improbable or impossible physical note appearances), and detecting zombies (decommissioned/known-destroyed numbers, and numbers never emitted). Randomly generating numbers is likely to trip clone and zombie sensors at various surveillance points.

Bill scanning to verify authenticity is already occurring, why not record the fact Bank of xAI ATM #67387 tendered two Franklins with serial numbers $SERIALA and $SERIALB to you (verified by PIN and card, and possibly bolstered by Face ID incognito); maybe older systems only do the verification locally and lack OCR, but I'm positive new systems are plenty powerful enough to run pared down OCR on serial numbers... wait they have been doing it with cheques all these years with handwritten dollar values, so why not OCR serial numbers coming and going? You see? The net deepens. I probably can't suggest methods of washing this data without possibly committing some obscure crime, so I will leave you to your creative imaginations...

99.9% of ATMs in the United States do not have bill scanning capability and are purchased for $1000-$2000.

Hyosung isn't putting this capability on these cheap units, neither is NCR on even more expensive units.