Barnabas is a great big fibber. There, 1795 all solved....
As for 1970/1840, I'm going to mention periodically my newfound conviction that Barnabas and Julia fixed history and therefore averted most of the events or relationships implied in 1970. Judah Stiles' real reign of terror begins after he becomes master of Collinwood. Were there any specifics about Roxanne/Gerard in 1970? I don't remember any of that.
Actually they fixed history and then re-broke it, in a different way.