I remember that 1975 Set as well. Not only did it have the BiCentennial Coins in it (two IKE Dollars) but it also had the "LAST" S Mint Cent. You see, since 1968, the San Francisco Mint had been producing Nickels and Cents and in late 1974 an announcement was made that the SF Mint would NOT produce any Cents for 1975. There were a LOT of Speculation Stories about how valuable this little cent would be. I know that I bought one. But I was young. And Dumb.
I wanted one set. Thought they were sold out yesterday and had to buy one on the bay for $48.50. Then they come back up today! I bought another one from the mint though.