The GGG types are all used with NOB C obverses but not with AVG . It seems that if Numerian were made Augustus before the death of Carus that the GGG coins would also be shown with AVG obverses. I would like to hear from someone with access to recent studies on this subject. This suggests that the GGG coins were issued when both sons were Caesars at the beginning of the reign and the mint considered the three honored persons deserving of the plural reverse even though only one was actually Augustus. This would be completely unprecedented but certainly possible.
Stamp collectors place special value on specimens well centered with extra wide margins.
There is a price paid for all that metal outside the beaded borders. The flan, weighing an appropriate 4.1g, is much thinner than usual. This thinness made it impossible for the striking process to fill the die detail on both sides of the coin. The reverse shows a flat spot in the center where the metal was needed to fill the portrait on the obverse. It appears that Jupiter is handing something to Numerian.