I once rode to Atlanta in a Slumbercoach on the Crescent in 1990, and they had a whole check-in procedure at the information desk in Baltimore. They checked my name off a big computer print-out of the passenger manifest, and told me where to stand on the platform to access my car. It was a pretty long train, with coaches, a diner, a lounge car, several sleepers, and the slumbercoach. They may have been running the separate section to Mobile at the time, too, but I don't remember now.