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if thats true then how are you detecting it on this coin?
The gray matte rough surfaces of the whole coin indicate to me that the coin was restored by using Nic-A-Date (or some similar chemical composition).
You can find detailed slabbed key date Buffalos such as 18/17-D, 16/16 in auction archives that have the same rough surface appearance from restoration. They are what they are and they are worth what someone will pay for them.