Case hardening is still done today by pretty much everyone (including S&W) on the parts that they have decided need it, even if you don't see the colorations left on the unfinished steel by the bone and charcoal method. There are many ways to case harden steel, including every amateur gunsmith's favorite "finish": nitriding (which is not a finish in any way, shape, or form).
To be completely honest most of the old school "knowledge" is probably BS, as it's virtually impossible to tell a through hardened part from a case hardened part just by looking at them.
But I'm sure someone will tell me they read so and so on the internet so what would I know.......