I have this 1977 S Lincoln Proof Penny and see that there is a Rim Fin on the Obverse Right side and a Rim Fin on the Reverse upper right side. I thought that Proof pennies are carefully inspected and not released with any errors? Is this rare to have a rim fin on both Obverse and Reverse of a proof penny? Second question is about the "S" mint mark. It looks a bit like a block "S" and not a clear "S". Is there something going on with this mint mark?