Remember, the general rule is that a card's final grade can only be 0.5 higher than the lowest subgrade, unless two or more of your subgrades share the lowest subgrade score then your final grade will be equal to that lowest subgrade. (See this blog post for more information about the general rule.)
But when one subgrade is drastically lower than the rest of the subgrades, the card's final grade can sometimes be 1.0 higher than the lowest subgrade. However, this exception to the general rule only applies to the edges and surface subgrade.
The Exception to the General Rule
A card's final BGS grade can be 1.0 higher than the lowest subgrade if: (1) the drastically lower subgrade is either the edges or surface; and (2) the aggregate of the other three subgrades compared to the surface subgrade must be greater than 4.
Below are some cards to illustrate these exceptions.
Surface
The general rule is that the card's final grade can only be 0.5 higher than the lowest subgrade; however, in the above Aaron Rodgers card the final grade is 1.0 higher than the surface subgrade. This is because the lowest subgrade is the card's surface subgrade, and the aggregate difference of the other three subgrades when compared to the surface is 5 (the math is (9-7) + (8-7) + (9-7) = 5), which is greater than 4.
Again, the general rule is that a card's final grade can only be 0.5 higher than the lowest subgrade but in the above Jose Abreu card the card's final grade is 1.0 higher than the lowest subgrade. That is because the lowest subgrade is surface, and the aggregate difference of the other three subgrades when compared to the surface is 4.5 (the math is (10-8.5) + (10-8.5) + (10-8.5) = 4.5), which is greater than 4.
The general rule is that a card's final grade can only be 0.5 higher than the lowest subgrade. In the above Cordarelle Patterson card the card's final grade is only 0.5 higher than the lowest subgrade. This card follows the general rule because although the lowest subgrade is surface, the aggregate difference of the other three subgrades when compared to the surface is 4.0 (the math is (9.5-7.5) + (8.5-7.5) + (8.5-7.5) = 4.0), which is not greater than 4.
The general rule is that a card's final grade can only be 0.5 higher than the lowest subgrade. In the above Tom Brady card the card's final grade is only 0.5 higher than the lowest subgrade. This card follows the general rule because although the lowest subgrade is surface, the aggregate difference of the other three subgrades when compared to the surface is 3.5 (the math is (9-8) + (9-8) + (9.5-8) = 3.5), which is not greater than 4.
Edges
A card's final BGS grade can be 1.0 higher than the lowest subgrade if: (1) the drastically lower subgrade is either the edges or surface; and (2) the aggregate of the other three subgrades compared to the surface subgrade must be greater than 4.
The general rule is that the card's final grade can only be 0.5 higher than the lowest subgrade; however, in the above Dan Marino card the final grade is 1.0 higher than the edges subgrade. This is because the lowest subgrade is the card's edges subgrade, and the aggregate difference of the other three subgrades when compared to the edges is 5.5 (the math is (8.5-6.5) + (8.5-6.5) + (8-6.5) = 5.5), which is greater than 4.
The general rule is that the card's final grade can only be 0.5 higher than the lowest subgrade; however, in the above Matt Barkley card the final grade is 1.0 higher than the edges subgrade. This is because the lowest subgrade is the card's edges subgrade, and the aggregate difference of the other three subgrades when compared to the edges is 6.5 (the math is (9.5-7) + (9.5-7) + (8.5-7) = 6.5), which is greater than 4.
Centering
The exception that the card's final grade can be 1.0 higher than the lowest subgrade if the lowest subgrade is edges or surface does not also apply if the lowest subgrade is centering. In other words, even if the centering subgrade is drastically lower than the rest of the card's subgrades, the card's final grade will still be only 0.5 higher than the lowest subgrade.
The general rule is that the card's final grade can only be 0.5 higher than the lowest subgrade. In the above Reggie Wayne card, the final grade is 0.5 higher than the lowest subgrade. This is because the lowest subgrade is the card's centering subgrade. Although the aggregate difference of the other three subgrades when compared to the centering is 5.5 (the math is (9-7.5) + (10-7.5) + (9-7.5) = 5.5) which is greater than 4, that still doesn't matter because the lowest subgrade is centering.
Corners
The exception that the card's final grade can be 1.0 higher than the lowest subgrade if the lowest subgrade is edges or surface does not also apply if the lowest subgrade is corners. In other words, even if the corners subgrade is drastically lower than the rest of the card's subgrades, the card's final grade will still only be 0.5 higher than the lowest subgrade.
The general rule is that the card's final grade can only be 0.5 higher than the lowest subgrade. In the above Aaron Rodgers card, the final grade is 0.5 higher than the lowest subgrade. This is because the lowest subgrade is the card's centering subgrade. Although the aggregate difference of the other three subgrades when compared to the centering is 10.5 (the math is (9.5-5.5) + (8.5-5.5) + (9-5.5) = 10.5) which is greater than 4, that still doesn't matter because the lowest subgrade is centering.
Centering and Corners are Weighted
More Heavily than Edges and Surface
What do all the above cards show? They show that BGS gives more weight to a card's centering and corners subgrades than the edges and surface subgrades.
That might be supported by the fact that BGS lists the centering and corners subgrades first on the card's flip, although perhaps they were just putting the different subgrades in alphabetical order too.
From a collector's point of view, putting more weight on a card's centering and corners condition makes sense. Those two aspects of the card are usually the most easily discernible to the naked eye, and the most influential aspect of a card's overall eye appeal.
