~~~ been restored are not considered "altered" as would be a modern-day casino chip.

Research shows us that carvers and businesses offered the restoring/repairing of both Ivory and MOP chips/plaques; Ivory being 'plugged' and their fractures being mended as well... and in the case of MOP, it's an acceptable art form (and was practiced by distributors/manufacturers such as CARO-Paris) to resurface/grind a piece in order to remove natural inclusions or even go as far as completely 'reworking' the piece in order to bring it back to its original state when damaged (of which none was done to dupe anyone; casino or collector).

I've filled many Ivory chips where its pigment became disloged... no reason not to, and its widely accepted.