It shouldn't have and I don't think it did. In my experience, CGC has lately tended to be pretty hard on tanning, much less hard on dust shadows. Without having bought the grader's notes, I would guess they considered this a dust shadow and, so, failed to hammer it.
I agree with you, though, that it's off-putting and the type of flaw I tend to avoid with books in my ballpark. Of course, this book is in a different ballpark -- actually, more like a different sport altogether.
Yep, but the spine has it as well. Yes, another sport altogether. Just doesn't justify the gift and it makes me wonder ...
edit: whether it is the submission or the submitter