Although the information given above applies for films scratched after processing, different effects occur for films scratched or abraded before, during or after exposure.
The area under the scratch can be desensitised or sensitised according to the pressure applied when scratched and whether before, during or after exposure.
The problem of identification is not quite as difficult as it might seem because the action of processing heals the scratches and we can see the healing by examination under a magnifying glass.