When I say "it's unusual to see", I mean that this extra level of anti-counterfeiting (or just specific accounting for every chip with a unique number) is unusual for that time period (1960's) and for rack chips in general.

If you want to dig deeper, here's some info to consider --
The order cards say that 15,000 $1's; 4,000 $5's; 4,000 $25's and 1,000 25c chips were ordered in this batch of HHL mold chips.

It's my belief that ALL of them were stamped with a number, except the 25c chips. With a numbering system of 1 Letter + a 3-digit number, you can get 1000 chips per letter. For example, A000 thru A999 = 1000 chips. So the $5's and $25's may have just used 4 letters (A-B-C-D) plus the 3-digit number, to produce all 4,000 chips of each number. And for the 15,000 $1's, you need the first 15 letters of the alphabet (A thru O, or perhaps delete "O" since it looks like a Zero, and substitute "P"; same for the letter "I" (looks like a One), so substitute the letter "Q".

The question is, are there any $5's and $25's with letters beyond "D", and are there any $1's with letters beyond "Q"? I think there may be, and at one time, I tried to prove or disprove my theory, but I couldn't get enough of them to say either way.

Now, as to WHY they took this extra effort and expense to number their chips, I think it has to do with the evolution of the Nevada Club into the Diamond Jim's Nevada Club, and the changing multiple owners during that time.

Check out the following "Over 50 Vegas" website, done by another club member. It's quite good on Las Vegas downtown history:

https://over50vegas.com/index.html

And specifically the 2 pages on (a) Nevada Club, and (b) Diamond Jim's Nevada Club:

https://www.over50vegas.com/113_Fremont_Nevada_Club_.html
https://www.over50vegas.com/109__Fremont_Nevada_Club_Diamond_Jims____.html

If you follow the dates, the expansion of addresses and marquees out front, and the changing names of owners, it's my speculation that the owners didn't completely trust one another. To prevent some "extra" chips being made and "introduced" into the chip inventory, they came up with this additional accounting scheme to ensure that a strict accounting could be done on all chips. Again, that's just my speculation.

I hope that wan't "too much info", but it's an interesting set of chips, IMO.