Right about Staggers and not Byrd - West Virginia had lots of clout and few passengers. The sleeper was still an ICC requirement - ironically the 1980 Staggers act paved the way to abolishing the ICC. B&O/Chessie System’s desire to abandon chunks of the old B&O line between Cumberland and Cincinnati also played a role in the train’s end. It actually lasted longer than some other LD services which only survived until 1979.
For some utterly unaccountable reason I seem to have acquired the thought that the ICC was formally abolished in 1966. Where that came from, I cannot really guess. Turn that ‘6’ upside down and it would make sense.