C, if you used KA’s unbleached cake flour, that would explain the results you had. Unbleached flour does not work well in Rose’s butter cake recipes.
Also, I think there may have been a problem with your pans having too much batter. The recipe (TCB, p.46-7) makes two 9” x 1.5” layers. For two 9” x 2” layers, you should have used 1.33 (1 1/3) times the recipe (in my edition, this is noted in the sidebar on p.47). If you doubled the recipe and baked it in two 9” x 2” pans, that would have contributed to the poor result. The pans should only be filled about half full, according to the recipe.
The only successful way to double this recipe (using round layers) is to bake it in four 9” x 1.5” pans.
Given your size pan, I don’t think there was a problem with the baking powder, just with the flour and the quantity of batter in the pan.
Hope that helps!