What you are seeing for sale are mostly salesman samples made before 2001. Chipco notched many of their issues in quanity and gave every salesman 5 to 10 chips. They did roughly the same amounts with Chipco advertising on the obverse of many issues.
Paul-Son did some but not as many.
BJ did very few.
NV Gaming clamped down hard on notched chips after some were cashed in by casino cashiers. At least one $500 got cashed in Biloxi.
At this time distributors are only supposed to make 2 notched chips, one to submit to gaming for approval of the issue and one to be kept in a locked safe at the distributor as a sample.

Notched samples can be made for the casino to see and test on the tables before the actual production is made. A casino rep must sign for them and take responcibilty for them.