1967 SMS 5c

The difference is that the Special Mint Sets did not use the specially polished dies used for proof sets. However, they were of better quality than the regular circulation strikes.

I don't know why no proof sets were created. The U. S. Mint behaved very oddly for those first three years after they stopped making dimes, quarters, and half dollars out of 90% silver. In addition to no proof sets, coins did not have mint marks, no matter where they were made. I think there was a concern about hoarding and a coin shortage, but I don't see how proof sets and mint marks would have made a difference.

Yup.... like Bilbo said there were "date freezed" coins. Because the US was running short on coins and president Lyndon Johnson decided to freeze the date on the coins as well as remove the mint mark to prevent hoarding from coin collectors (like karrlot said).

Stephen, just think of it this way: You paid for a certified set of coin for less than $20, that's a good buy. You can put it up for sale and make a couple bucks or save it for your kids. Since they are certified coins... you dont have to worry about the grading and authenticity of the coins.

Enjoy.