A piece of the raised portion of the die breaks off and doesn't leave an impression. You can see the hat had a broken outline on the earlier chips; probably designed that way, but made the die weaker in this area. I also believe that's what causes the "E"'s turing into "F"'s on this and other CIC chips. They aren't one-time differences so I'd call each a new variety.

However, I can't see the differences in the surface finish that you mention on the plastic and metal. Might take a look at the actual chip to see these differences. Could be a new lot, or could just be surface wear on the molding or coining dies.