Leon,

I'm not going to name names, but that is not the information I have, which is first-hand info coming directly from those involved in inspecting the card when it was first submitted to PSA. Their head grader at the time was a friend of mine who I did a fair amount of business with. So if you were told something else, the story has changed.

From a common-sense perspective, I find it hard to believe that PSA could not know it was trimmed, the trimming IMO being so obvious to anyone experienced in T206s. In another thread about the card, one poster, an experienced card dealer, said he was offered the card at the Willow Grove show where Mastro took it immediately after purchasing it from Sevchuck, and he (and others) turned it down precisely because they thought it was trimmed.

Variation on a theme, I grant you.

The weird thing with that first point is that in a different hobby I had an expert examine two different items in person at an international show.
The opinions that had taken me some non trivial amount of time to reach were correct. But it took him probably under 2 min for one and under 30 seconds for the other. One I thought was not what it seemed in a bad way, the other I thought was good. (The good one has since received a certificate, that hobbies equivalent of tpg just without the grade)

The stuff was more involved than trimming of cardboard.

I see you were using "slabbed" literally. I did not know he was there in that capacity, had not heard his name associated in any way with the original grading. I do know he saw the card later when it was reholdered and I've heard his opinion of it.