Originally Posted by
JackJohn
my question here is: is it more likely the damaged cup threads got to work more or less properly, or that I rather deformed (damaged ?) the frame shell threads?
Bottom bracket cups are hardened steel, while the bottom bracket shell is not hardened, so it's easier for a misthreaded cup to damage the shell threads. Still, your pictures show a good number of undamaged threads on the cup, so as long as you can install it straight and secure, it should be useable.
PS: it’s French threading, so unlikely I can retap the BB just the same
As mentioned above, a sacrificial cup can be converted into a thread chaser tool. But if the shell threads are too badly damaged to securely hold the cup, you still have a couple options: 1) a threadless bottom bracket cartridge as from Edco, Mavic, YST, Velo-Orange, etc. or, 2) reaming the shell and tapping fresh Italian threads into the shell to use a standard Italian thread bottom bracket or cartridge.