I'm having a helluva time getting this to show up larger, as there is something off with my imgur account, so I'm stuck using this little one.
The main 'problem' here is the PSA 10 slab seems to have been stretched a bit vertically. In other words, when the two pictures I used (grabbed the PSA 9 and 10 from the OP) were size-matched side to side (black box), the PSA 10 image was a bit taller than the 9. It seems the scan used was 100% side-to-side, but probably 102% (something like that) top-to-bottom. Hope that makes sense. That stretching made the white side areas appear thinner. So I 'un-squooshed' it to return it to (theoretically) 100% side-to-side AND top-to-bottom, and here is what the comparison looks like...
This may lead to the larger version:
https://imgur.com/a/igasSA2
(I obviously have no horse in this race, as I can't even afford a child's drawing of a '52 Bowman Mantle.) It would appear that the stretching of the image vertically is what caused it to very much look like a trim job side-to-side, but when 'corrected' it seems a heckuva lot closer to fine. However, top-to-bottom could be (depending on what sort of variances naturally occurred in the heights of these cards during the cutting process) a different story.