I suspect that earlier, shorter sleeper DC-6s were operated in a single-class, all sleeper configuration, like the BCPA examples. There is a photo on the Wikipedia DC-6 page of a SAS aircraft with the same window layout, and that's also an early, short-fuselage DC-6.
American, Pan Am, etc operated mostly the longer DC-6B and I'm guessing that they would have been in a two-class configuration with sleeperette seats only at the front of the cabin, hence fewer upper windows.