>None of this works if the serial numbers were recorded when the cash was put into the vault.

There are workarounds even for that, such as shipping the money overseas and using it in places that love US dollars but don't much care for cash transaction reporting rules.

However, I doubt any group as apparently pro as these guys, who seem to have known exactly what to hit and when for a ton of money, would have done so without first also verifying that the serial numbers weren't recorded. I'd bet that they werent, at least not yet.