It is the collectors who make their own decisions based on their own personal preferences and subjective views. Yes, there are certain guidelines to follow, such as pitting, evenness and colour.
When I examine my Lange Anniversary under the loupe, it is "near perfect". I dare not say perfect. No bleeding at the XII roman numeral, Almost free of craters (unlike PP5115). Very nice cream colour. Of course, I am not in the position to say this for the rest of the pieces.
Thomas, I am afraid I can"t agree that it is considered the medium grade work.
What I can say is that the quality of every piece of the enamel dial varies. Even I am not happy with enamel dial of Zheng He piece.
Regards
Ling