Hi John- when I'm not breaking ice or digging up snow, I'm doing fine.
I had the same thought you did: for a high profile card such as a T206 Plank, there should be some kind of database where a grading company can trace the past transactions of a particular card. But it would be difficult to keep up, and so many transactions are private. And where does one draw the line? Sure, you would like to think that every Wagner and Plank could be traced back. But what about a T206 Lajoie? How about a 1933 Goudey Hornsby? As I said, it would be a really tough thing to do.
What the grading companies should do is spend more time grading expensive cards. I'm not completely sure the removal of this stain would have been detectable under high magnification, but for a card worth well into five figures, if I'm a grader I want to do my due diligence. Obviously, I can't say the grader was negligent, but it's possible he missed something that could have been detected.
And yes, a cleaning should have lowered the grade from an SGC 30 to a PSA Altered...if it was detected.