Jaime Hernandez: The 1970 No S Proof Roosevelt Dime was the second year in which a Roosevelt Dime was accidentally struck without the S mint mark. The Mint accidentally struck Proof Dimes without S mint marks in three different years which are 1968, 1970 and 1983.
The first Proof Roosevelt Dime struck without an S mint mark was the 1968 Proof No S Dime. The 1968 Proof No S Dime is the scarcest of all three different No S Proof Dimes struck, as there are probably about a dozen or less known. The 1970 and 1983 No S Proof Dimes are similarly scarce with about 500 or so examples known.