@tdelios It don't think it wise it would mean that everytime you make a error in your manual scrape your image and gamelist.xml part related to the not found game would be deleted and you would have to do it all over again.
Besides as not found games don't appear in EmulationStation and images are so small compared to modern SD cards, USB sticks or HDD it's not really an issue.

It's also simpler to do your scrape once you have manually remove every game you didn't want than doing before