The purple looking toning at the bottom of both sides is synonymous with dip residue that wasn't completely rinsed off. Over time, that residue starts oxidizing and attacking the metal.
My guess is NGC overlooked it or determined it was something else. If the residue keeps getting darker and darker over time then you'll know for sure what it is.
My guess is NGC overlooked it or determined it was something else. If the residue keeps getting darker and darker over time then you'll know for sure what it is.




















