Properly processed & stored b&w *is* archival, being usable pretty much as long as the film stock lasts. IIRC there was at least one color process (very expensive) that was similar. Kodachrome overall is pretty good. Most color isn't.

Digital is archival but not in the sense that you put it in a box and forget about it. Your film (correctly chosen and processed) and vinyl records might last longer under those conditions. Even if your CD is physically readable, it probably won't actually be readable in 100 years due to loss of drive mechanisms and decoding information. OTOH, digital is easier to copy with zero errors than physical film, so with attention it *is* archival in the sense of the data being migrated as it grows old.

Is 100-year archiving of MSTS .exe and data files necessary? Isn't it likely that the software will become unusable at some point and data will have to be migrated to something like Open Rails that's more modern to keep using it? And isn't that migration, if it allows the data to still be used, not a form of archiving?