Could be a filled die (a part of the die was filled with something,) struck through grease (there was grease on the die or planchet when the coin was struck,) or the die was used too much and those details wore off.
I'm leaning towards and overused die. A filled die is possible, but that would be a very small detail to get filled. If it was struck through grease, I think more of the strike would have been affected.
Someone else should be able to help you out with the values.