Thanks everyone. And especially Brian. I finally found the flaw. There's a very slight bend, running roughly along a line from the bottom of the C to the lowest uniform button.
It's only visible under certain lighting conditions, especially in the holder.
Bright natural light and Halogen didn't make it visible, only muted natural light at a very shallow angle. It shows as a difference in gloss from one section to the next. If I had to guess, the difference from the cardboard being flat is probably less than a degree, probably much less.
I'm pretty impressed they were able to find that. I did a very close examination before sending it in. And obviously a few after to try to figure out the grade. Plus I've had the card for over 20 years. It makes me feel much more confident in the other grades too.
I know it's probably mostly trade secrets, but I'd love to know what the overall process of grading is. In other words, what gets looked at in what order. And maybe take some of the training, maybe some sort of seminar? I think that would be very interesting. Lots to learn beyond the familiar system.
I'll be adding scans to the registry, mine is STB206. Not many graded yet, as many of mine would only be 10s (And I'm very confident about those
)
Steve B