M-Train
Member
I would not be sure that either is right, though combined, the right idea should be almost there.
The two numbers reflect inconsistencies in the application of BR renumberings: as @xotGD notes, they indeed were not ‘real’ numbers, but it is not the case that both were used in preservation. The loco that actually bore 90733 in BR days (if very briefly) was not an Austerity, and no loco ever did carry the number 32643, in BR or preservation.
The two numbers reflect inconsistencies in the application of BR renumberings: as @xotGD notes, they indeed were not ‘real’ numbers, but it is not the case that both were used in preservation. The loco that actually bore 90733 in BR days (if very briefly) was not an Austerity, and no loco ever did carry the number 32643, in BR or preservation.