Get me a piece from a Gen Rolex and I would be more then happy to take a run at it. However, I think you would find the they due use 904. Could you imaging the fall back on them if it was ever discovered they used some other type of Stainless steel?
904 from a practicality stand point is nothing special. It is jammed packed full of Chromium, Nickel, Molybdenum and a splash of Copper, making it the best protection for high chloride and acidic environments. So unless you are a saturation diver or swimming in sulfuric acid, for all practical purposes, 904L would serve most of us no good in our time pieces. Throw nitric acid into the mix and you would much rather have 304L.
If I could engineer my own time piece out of any material I could choose. I would chose a 440C. 440C SS has slightly less resistance to chlorides as 304, however the strength and hardness is beyond comparison! Scratches, marks, fine swirls