Sorry to belabor this point but there is something I don't understand. More specifically, what's wrong with cold setting the ST/DT/BB shell assembly back to the proper angle and moving forward with the build?

If I'm building a frame and braze the ST into the BB shell and then check alignment using my surface plate, and the ST is 9mm low where the seat cluster will lay, I'd be perfectly happy to bend the tube to straight and continue with the build. Am I a heathen here? Assuming no (hopefully), then what's different in this situation? It seems to me you can simply spread the angle, which will divide the cold setting between two tubes, not just one. Any "bowing" of the tubes would be so small as to be negligible.