Date of production is most likely correct since it's duplicated on the card and your mention of casino opening is certainly correct which is not unusual for an order being placed produced/shipped far in advance.

We know of several chips/plaques that came out of the CARO Collection (via Serge and whomever) that are unknown by anyone; collectors or casino owners/operators and not mentioned or included in ChipGuide by request of buyers. This is all visible (archived) at the
time I posted some of the chips both Eisenstadt and I bought from Serge away from eBay and, I am sure there were others who did the same at the time (and afterwards).

Though, I will not discount the gray/white insert notation being a typo... nor do I know if other examples of what you have are known...

Example: We know of many colors from USPC which were not in Herz' original photos of what we assumed was the complete run.