Won't a hardened bearing cup dull your expensive thread file, without even being improved much in the process? Dunno, never tried it myself. And never will, unless someone else is paying for the file!

I have used thread files, but only on bolts and other non-hardened applications. Like on a cheap BB cup, but not on a Campy

I might try a fine triangle file on a Campy cup, since they're cheaper and easier to come by. Filing a thread with a triangle file takes more skill and good eyesight, but you can concentrate your filing on only the part of the thread that needs filing. Harder to do that with a thread file, that files on several threads at once. The triangle file needs to be a fine one because coarse files have too much of a radius where the two sides of the triangle meet. They can't file down into the bottom of the thread "valley".