Also, PSA doesn't tell you the subgrades of what each aspect graded (corners, edges, centering, surface/creases, registration, etc).
BGS will tell you the grades of each of those components, and their normal rule of thumb is not to give a grade higher than +1 of the lowest component score. They don't put this on their Vintage cases, though, and their dividing line is 1980.
Here's an example:
1981 Kellogg's 3-D Super Stars #5 - Mike Schmidt [BVG*9]
Courtesy of COMC.com
If the surface was a 4 instead of 9, the highest this card could get graded is probably a 5.