"YEP'' Getting notes graded by a TPG company, is like deep sea fishing!!. You never know what your going to catch...
That 58Q to 66Q is exactly the point about grading. There may not have actually been a fold, but maybe someone saw something that they thought might be a fold.
Recently, I have crossed several 58Q PCGS notes to 65Q PMG. I bought them raw and they were all Gem CU - no folds, bends, etc. But, PCGS decided otherwise. So, eventually, I cut them out and submitted them to PMG, where they were correctly graded.
But, I've also had the opposite experience. A PMG 64 flat that was original Gem all day long, that crossed to 66Q.
Graders do their best, but have good and bad days, or just see things differently. Don't harbor the illusion that TPG is a science.