It's a form of additional security / anti-counterfeiting in which the chips were stamped with a non-recurring alphanumeric numbers. They did this for $1's $5's and $25's.

See examples on the ChipGuide page linked here:
http://chipguide.themogh.org/cg_chip2.php?id=NVLVNC&v=1067228743

Besides the chip pics, the order card is shown, specifying a large print on one side and a smaller print on the other side. The smaller print leaves room for the alphanumeric stamped area, so it appears the stamping was planned in the chip's design, not an afterthought.

I don't know which letters & numbers were used on each denomination, and it is unusual to see.

Also, I'm pretty sure that the Nevada Club had a whole group of individuals that owned portions (or "points") of the club. The numbering could have been to insure that no one had extra chips made to be "run in" to the game and dilute the club's total face value of chips on hand.

Further note that this series of chips was produced on the HHL (=Horseheads LEFT) mold, which is less frequently used than the HHR mold. Is that significant? I'm not sure. Perhaps.