This Summer 2006 NHRS Bulletin provides much detail about slumber coaches and is a must read for you. https://www.train-museum.org/w...7/SlumberCoaches.pdf
While it provides car roster, and train names from two different Official Guides, it does not say which cars names were in which trains. A caption in Craig Bossler's B&O Color Guide to Freight and Passenger Equipment agrees with the source you cited.
He says the B&O's first two purchased cars, Slumberland (7700) and Dreamland (7701) were used on the Columbian, while the three leased cars, Sleepland (7703), Thriftland (7704) and Restland (7704), were used on the National Limited. He prints two photos of Thriftland taken at St. Louis Station.
