Silver eagle registry set coins

I have a few problems with the found in this set need someone to explain why there is error coins in a basic set ,yet there are not conis that should be in there are not ? Example the 2008 reverse of 07 that's an error coin at least I think it is ,and the 2013 S is not in set? And then you have the 2011S that is not really an S its a P? Help me before I lose my mind .Jay