I admit I haven't read the whole thread yet, but will soon... I do have comment though
I see your point in not being able to source *Rolex's* 904L, but the factories are in China, where there are many, many (many) steel mills.
If one orders 904L steel (which we all know the composition of), they can souce the 904L steel directly from their choice of mills...
The only way we can know if these cases advertised are actually 904L is if we send a case to a metallurgist and have it tested... Then we can call them liars, or not.
I suspect the forging, machining, and finishing processes would be more involved and expensive with 904L... but I think sourcing the ingots wouldn't be so difficult if it were purchased in bulk... The cost would be in the product manufacture.