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Don JI believe SGC's policy on writing on the back boils down to this:
1 line of text: Best Grade: SGC 30
2 lines of text: Best Grade: SGC 20
3 or more lines of text: Best Grade SGC 10
Doesn't matter how nice the card is otherwise on the front; a card's other attributes can bring the grade down from a 30 or 20 as well.
In looking at the stamp on the back of the Green Cobb; it looks like they counted the initials as three distinct lines of text.