Well, if you punch in over a track that already has content you are deleting previous content via the eraser head, so there's no undo for that. Unless you have

Well, if you punch in over a track that already has content you are deleting previous content via the eraser head, so there's no undo for that. Unless you have "backup", which is obviously a second generation recording. If you "fix it in an overdub", then maybe but it makes mixing more difficult. Or you gotta do a bounce which is, once again, second generation. Of course something being second generation is not the worst thing in the world, but if you bounce a lot, noise and distortion will creep in.