Middle Ground Question

Good day to all. O.k., so the two main TPG's use "EPQ" and "PPQ" as a quality of paper notation. By the same token, they use "NET" and "APPARENT" when there is an issue, i.e.,"tear","rust","pin-hole","stain" and so on. However, when a note has no "EPQ" or "PPQ" designation, but also isn't dinged with a "NET" or "APPARENT", then what is preventing the note from receiving "EPQ" or "PPQ"? At first I thought "bends" or "creases", but as a quick example, I have a $1 1923 Red Seal graded VF-35 EPQ. And I can clearly see the three folds/creases. So I'm at a loss to understand the middle ground. Thanks much for any thoughts and/or help.