NGC 1986 silver American eagle struck thru 3M sanding disc reverse. The coin was struck thru a round emory disc on its reverse, with the strike thru leaving a rough, granular impression of the emory disc in the coin's surfaces. It is known what they are struck thru because examples of the struck emory discs are known, and they are made by the brand "3M."
Very scarce, with around 6-7 known in our estimation.
NGC 2017 silver eagle struck thru and retained finned rim reverse. The coin has a long, thin sliver of silver metal struck into its reverse, which is from this or more likely another coin's "finned...
NGC 2017-(P) silver eagle clashed dies obverse and reverse. The coin shows strong die clash marks on the obverse and also lesser clash marks on the reverse.
A scarce year for die clashes...