Okay, I found a more extreme example and IMPLORE some knowledgeable soul in this community to explain the rationale for the back centering. this card was sold in an REA auction and I want to point out that this is not intended to cast REA in a negative light, I in fact have dealt with them before and they are terrific, it's just a really really good example of something I am trying to better understand:
http://www.robertedwardauctions.com/.../2009/605.html
1948-49 Leaf Paige, PSA 7, the description refers to the back centering as 10/90 but wow it looks something closer to 5/95. According to PSA, a NM 7 should have back centering no worse than 90/10...
thanks in advance for your help!