~~~ "filled-in; drillhole (plugged)" gambling chip is acceptable is with an ivory chip where a nervehole is drilled and plugged with actual ivory in order to prevent further fracture and possible cracking... this practice is also done with ivory pool/billiard balls as well as with draughtsmen.

The two draughtsmen seen below are of solid Afican elephant tusk ivory (not laminated); they're huge... 45mm wide and 15mm in thicknes with a deep 5mm concave center field, and both are free of any nerveholes or fractures (or plugs). I do have examples that are edge-chipped and center fractures.
I've placed two of these sets in two of the world's most outstanding ivory collections known.