Hi, I really like these kinda watches, but my knowledge is not that great. These subdials does not look great, more like the moldy tomatoes you'll find far back in my fridge. Normal wear and tear that you could do something about, or a big no no?
The dirt is most likely mold that's under the clear coat. The only way to clean it is to remove the clear coat and clean it off, then reapply clear coat. You can only hope you get lucky with a solution of cleaning fluid that doesn't damage the paint while stripping off the clear coat and then the dirt / mold.