The mistake is relying on grading company numbers as anything more than helping identify hidden flaws in a piece of cardboard. If you're relying on PSA or SGC to tell you whether a card is off-center, you're really missing the boat.
For me, I have traditionally played in the PSA 5/SGC 60 area of the T206 market. I also really dislike spider wrinkles and light creases. I have never -- really never -- seen an SGC 60 T206 card with a wrinkle or a crease. I would guess they exist, but it certainly is not common.
On the other hand, I once tried to cross 40 PSA 5 T206 cards over to SGC, and only 30 of them made it because of wrinkles and creasing in the remaining 10. That was 10+ years ago, so maybe standards have changed.
SGC has always been easier on corner wear and tough on creases, which I appreciate more than tough on corner wear and easy on creases because corner wear is obvious. Creases are tough to see.
So, I do not think it matters whether TPGs use the same numbering, provided you know what to expect by the standards each provide before purchasing a card encapsulated by one of them.
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