I wouldn't describe it as faking if the work has been done properly by an experienced person/gunsmith/armourer. But clearly the resulting gun isn't the same thing as a gun where all the serial numbered parts match and none have been changed since manufacture. That is why I believe that we need some words to describe a gun where the numbers have been changed to match. If "forced matched" is not acceptable then we need some other phrase to describe it. It doesn't really matter what the phrase is provided it is different from "matching numbers".
My opinion only.
Anything other than a part officially renumbered/replaced by an armourer during military service can't be called "matching".