They can be damaged in a number of ways, but wear seldom shows itself on the chips because they are so durable. The only exception applies to the early CIC chips which were made with black-filled incuse lettering on the coin. The black will eventually start to flake off, although I suspect some of those seen today with partial paint in the letters are the result of misguided efforts of a collector to "get the dirt out" of the lettering [g].