Otherwise, well, the numbers are -(old start line number),(old line count) +(new start line number),(new line count) for the entire hunk introduced by @@ (whether it contains one group of changed lines or more). I'm sure you see how to fix them up, but accumulating a line number shift as you go through the file sounds very fiddly and error-prone. It also sounds like something the computer should be able to do for you (given the old patch and the new messed-up patch whose hunks correspond one-to-one to the old).