You are correct. Both surfaces must be flat. I often worked on that as well using extra fine sandpapaper. I think 400.This is another situation where if it always works for you I can't say you're wrong(especially with that resumé!), but I will add my experience. To me it is similar to the instructions for would glue. You want two smooth surfaces. Less is more with the glue in this case. If the ferrule has imperfections then you gotta do something to the ferrule, but if both surfaces are flat and smooth, you shouldn't have to do any scoring.