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JimBThough I posted this on N172 thread, I think it is equally relavent here.
With regards to comparisons of grading standards, the ONLY way to determine whether SGC or PSA is tougher or more lenient is to send them both a large sample of the exact same cards and compare on the basis of the grades they assign to those cards. If I send a nm card to SGC and they grade it 84 and somebody else send a vg card to PSA and they grade it a 3, does that mean SGC is more leniant? Of course not. Drawing conclusions based on averages when they have graded completely different cards is utterly unscientific. There could be a hundred reasons to account for the discrepancy. Who knows what motivated the hundreds of different submitters to choose the grading company they did and how that all fleshes itself out in the overall numbers.
JimB