[jchcollins]

SGC recently is murderously tough on centering. Even tougher than their documented standards in some cases, I have observed. That affects most, but not necessarily all cards in their newest "tuxedo" slab. The did give your card the .5 bump, so they were not as tough on the centering here as they could have been, and that in itself is suggestive of the fact that it's likely not centering alone which led to the grade. I'm guessing as others have suggested that you are missing a crease or a wrinkle somewhere. Again, this is where "buy the card, not the grade" comes in heavily when considering eye appeal. Particularly for the larger mid-50's cards, I think many in the 3-4 range have the capacity to retain huge eye appeal. Perhaps it's because most were printed on thicker cardboard stock than say, Topps was using when the late 60's / early 70's rolled around.

Sometimes the graders miss, or leave a mystery though. Last year I had a '67 Mantle that I thought had a chance at a 6; SGC gave it a 4. There was little wrong with that card besides a moderate centering shift. No creases, sharp enough corners for a 6 easily. They could have found something I didn't under magnification, but even so it was a very tough grade. That just happens sometimes.