Just as the notation of interior tanning benefited you in your grade estimate, more detail on crease length would benefit all of us. As you point out, usually its not just one substantial defect on a book that determines grade; instead, its a combination of defects. So, if an auction lists a 6.5 book with grader notes that say, "multiple light spine creases, does not break color and light crease lower right front cover, breaks color" would it not be more informative if it said instead, "multiple light spine creases, does not break color and light 2 " crease lower right front cover, breaks color"? If the damage to the book is not evident in the auction picture, one description you might roll the dice and see if a press could upgrade the book and the other, probably not. Alternately, if you do not like pressing, one description hides the 2" color break that you might be unpleasantly surprised by, book in hand, while the other one informs your buying decision.
More info on defects is always a good thing; well, at least form the buyer's perspective.