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Marc S.I usually don't look. I'm assuming from your e-mail that your experience is specifically with PSA, and not with SGC. That said, perhaps it would be a good/interesting data point, but I'm not sure how to develop actionable items out of it (other than to become paranoid and bit on a lot fewer cards). This is further mitigated, in my mind, by two factors:
A) I tend to think that higher-dollar, higher-grade cards often get submitted in smaller submissions, so there is a larger probability that there may not be ample surrounding certification numbers to provide a sufficient sample size.
B) Memory Lane has taught us that it is perhaps easy for some sellers / auctioneers to simply get the serial numbers on their PSA graded cards changed. If nothing else, this can completely invalidate any analysis along these lines.
Perhaps it's just blissful ignorance on my end. But I tend to trust a combination of my eyes/experience, augmented by the professional grader's stamp of approval.