~~~ since I doubt anyone would drill their own MOP set when done with it and they were probably drilled early on because I have seen so few drilled MOP chips with the exception of what someone drilled for a keyring or jewelry...

BTW, serial numbers on chips don't really determine that they are from a casino because engraving houses constantly replenished their stock inventory with engraving denominations on the reverse while keeping the obverse blank (some finished shapes show us this), even with and without serial numbers and if so requested with an order; monetary units could easilly be engraved and placed in their proper position.

Overall; a bit unusual even for casino inventory to he found drilled since manufacturers bought obsolete inventories to grind away a face for later use and, that's one of the reasons we see those thin chips and plaques or the ones where just the central field was ground down to later receive a new engraving and still have the overall thickness/weight desired unlike the the PAU material which surfaced in several stages of reconstruction.