The more I look, the more I think it's a freak reflection. (Look at the images on the top right lug,) Tarnish like this on an 18kt Patek Philippe? Nah.
I think you can get most of that out with hand polishing with a dry polish cloth. It won’t polish out the scratches, won’t cause any fading of the hallmarks etc. The aging of the dial with color change is the type of patina I wouldn’t want to mess with. ...