Originally Posted by
oneclick
If a damaged cup damages the shell threads it is likely to remove material. The good cup will still fit, but the fit will be looser.
I'd get rid of any thread sections that were bad, down to the thread roots - a part-circle of thread is worth keeping, though it may make initial alignment a bit tricky.
And likely yes, rule of thumb is that most of the load of a threaded fastener is taken by the first three threads.