I had heard that A2 and B52 were siblings, but evidently that's not the case. Someone asked Jeremiah and he contacted Henning von Schmeling about the history of these two plants and this is what he said:
Jeremiah Harris wrote:Henning von Schmeling selfed Carolina Giant and got 7 seeds. These were labeled A-1 through A-7. The largest, A-3, was seledcted and back crossed with the parent plant, Carolina Giant, producing 78 seedlings that were labeled B-1 through B-78.
After 6 months, one plant far outgrew the rest of the batch and ultimately produced giant traps. It was labeled B-27, which wasn't appealing to Henning, so he switched the labels between B-52 and B-27 and the name B-52 was given to the biggest of these plants.
So, evidently, A2 is a great uncle/aunt of B52. A3 is the parent plant of B52, but I've never seen this plant in cultivation anywhere.