This also underscores one of the significant differences in philosophy between PMG and PCGS. PMG net grades for defects such as graffiti, foreign substances, etc. which means they reduce the overall numerical grade to account for these. PCGS does not lower the numerical grade but notes them as apparent.
Here is the hypothetical. The last two notes in a fresh pack. The higher number has a foreign substance and the other doesn't because the higher number is on the outside and picked up glue or whatever from being set down. But the paper for both is otherwise a 66. PMG will grade the one without the substance as 66 EPQ and the other as Net 64 (or whatever their standard determines the downgrade should be) without PPQ. PCGS would grade one 66 PPQ and the other Apparent 66 with no PPQ.
Neither of these is wrong and both philosophies have their merits . It is simply the application of each company's standards. PCGS refers to PMG's method as market grading; that is, giving a lower number because the one with the defect should bring less money. But PCGS method has led to some otherwise absurd grades such as a note with one quarter of it missing being graded in the high 60s because they only grade the paper that is there.