back-up set of chips to the primary set. (Arizona has this requirement.) Beyond being a requirement, it makes good sense. If a casino operator knows, or even suspects that their chips have been counterfeited, then, within a matter of minutes (conceivably) all of the primary chips can be pulled and replaced with the back-up set. At that point, any and all customer hand in of chips can be scrutinized for validity.

Some houses will have a back-up set to the higher denominations only. Some houses will use an older issue as the back-up set.

It varies from house to house and jurisdiction to jurisdiction.

I hope this helps!

Jim