By the positioning of the scratches and the break between the two lines I thin it can be ruled out that it was due to grit or other damage before being processes. Also it it had been done before processing there would have been physical damage to the 'raw' film which I know would have removed one or more colour layers and even gone right through to the base layer and been rendered clear film. (Been there, seen it, and done it myself that's how I know) The Lab has a few answers to give.