During the period of the "missing episode," the series was being repeated on one of the Washington D. C. stations (I believe) in the evenings (I think this would have been Channel 7? Channel 13 was ABC's Baltimore based station which was where I watched DS from 1968 through the end in '71). IIRC, they ran it at 11:30 at night. I seem to recall some of the shows being repeated on Sunday nights as well. It stands out in my memory because until the 1990s, this was my only opportunity to see any of the episodes more than once (I did videotape one on a visit at my parents' home in the 1980s, I think). The shows I saw in the first 1976 syndication were brand new to me--from 1967.
Anyhow, since those shows were being re-shown in other markets, it's possible that extra copies were made of those final weeks of the PT 1841 storyline. So, yeah, one could show up one day. It seems unlikely at this stage of the game, but who knows.
The one I want the original color master of is the debut episode of Countess du Pres and Angelique from 1795. I hadn't heard about the recovery of a color master from the 1970 sequence.
G.