Tim P. asks: Why no Philadelphia Nickels for 1968 – 1970 and is a 1970 S a Proof coin?
Paranoia by the treasury. The government wrongly blamed coin collectors for the severe coin shortage of 1960-64 and banned mint marks from 1965 to 1967. The mint grudgingly resumed placing mint marks on coins in 1968. The Philadelphia Mint specialized in minting large numbers of copper-nickel dimes and quarters to replace the silver coins that were pulled out of circulation by the public. The branch mints worked the most on cents and nickels which had no precious metal content. No nickels were made in Philadelphia during this period to allow more time for the coins needed the most.
The 1970-S nickel was minted both as a business strike and as a “S” mint proof.