For example, a card with Centering 9.5, Corners 9.5, Edges 9.5, and Surface 9.0 will receive a final grade of 9.5. A card with Centering 9.5, Corners 9.5, Edges 9.0, and Surface 9.0 will receive a final grade of 9.0.
This rule will work for about 90% of BGS graded cards. Now, about that other 10%...
Sometimes, when one subgrade is drastically lower than the rest of the subgrades, the final score can be higher than 0.5 more than the lowest subgrade. This is especially true of the surface subgrade.
The surface subgrade in BGS grading seems to be weighted the least of the four subgrades.
Take a look at the following cards which received a final grade higher than 0.5 more than the lowest subgrade.
Applying the general rule to the Aaron Rodgers card, it should have received a final grade of 7.5 because that is 0.5 higher than the lowest subgrade, but the card received a final grade of 8.0!
Applying the general rule to the Jose Abreu card, it should have received a final grade of 9.0 because that is 0.5 higher than the lowest subgrade, but the card received a final grade of 9.5!
What's going on here?!
The surface subgrade is one of those weird exceptions where if it is drastically lower than the rest of the other subgrades, the final grade can actually be 1.0 higher than the lowest (in this case the surface) subgrade.
But what about the following card?
The surface subgrade on this Tom Brady card is 8.0, and is lower than the other subgrades by 1.0. Yet this card's final grade is still a 8.5 and not a 9.0.
What's going on here?!
As far as I can tell, there must be some hidden rule coming into play for the Tom Brady card which prevents its final grade from being a 9.0 despite the fact that all the other subgrades are at least 1.0 or higher than the surface subgrade.
My guess is that the aggregate of the difference between all the other subgrades and the surface subgrade is what determines if the final grade can actually be 0.5 higher than the surface subgrade, or get bumped up 1.0 higher than the surface subgrade.
For example, on the Aaron Rodgers card, the aggregate difference between all the other subgrades compared to the surface is: (9-7) + (8-7) + (9-7) = 5.
On the Jose Abrue card, the aggregate difference between all the other subgrades compared to the surface is: (10-8.5) + (10-8.5) + (10-8.5) = 4.5.
But, on the Tom Brady card, the aggregate difference between all the other subgrades compared to the surface is: (9-8) + (9-8) + (9.5-8) = 3.5.
So, based on these three cards, it appears as if the aggregate difference between all the other subgrades compared to the surface must 4.5 or higher for the card's final grade to get bumped up 1.0 more than the surface subgrade rather than the usual 0.5.
It is possible that the aggregate difference between all the other subgrades compared to the surface must only be 4.0 or higher for the card's final grade to get bumped up 1.0 more than the surface subgrade rather than the usual 0.5, but since we don't have a card with those exact subgrades I cannot confirm that theory.
So, what does this all mean?
I still think the general rule that your final BGS score can only be 0.5 higher than the lowest subgrade is still the easiest way to remember how 90% (or more!) of BGS grades will work; however, I think it's good to know and keep in mind that the surface subgrade is one of those exceptions. Remember, if the aggregate difference between all the other subgrades compared to the surface is 4.5 or more, then the card's final grade can be 1.0 higher than the surface subgrade.
