The "missing money" shown on the Horizon system was never missing it was created by bugs, errors and defects in the system, one example is that in certain circumstances when a postmaster rolled over from one week to the next the system would add phantom stock to the file that didn't exist. So the following week when the postmaster balanced it looked like that stock was missing. In other words the cash and stock the postmaster had was correct it was the system figures that were wrong. There are now 43 known errors that would create phantom stock/cash.
The postmaster paid back the "missing" cash. It is now known that this cash was held in a suspense account for a period of time but then transferred to POL bottom line. So they effectively stole money from postamsters!