in the parallel-time topic recently someone stated that the writers seemed more concerned with what impact a particular situation would have on
that day's episode than whether or not it fit into overall series continuity or made any real sense even within the DS world.
the reason for this being the presence of quentin and angelique in 1970 parallel time. the whole premise of the storyline was an alternate version of the "present" where the characters lead different lives based on making different choices. in some examples they follow through with this setup. for instance "hoffman" could legitimately be a variation on the julia of the present who became, for whatever reasons, a maid rather than persuing a medical career. but it's the same person.
however quentin and angelique don't legitimately have any counterparts in the "present". they are not actually extant. they only exist there through various supernatural manipulations but they are not truly "part" of that time.
however the impact of this storyline comes from their participation. it could be the same case with 1840. the writers just thought the impact would come from angelique's presence, the DUH-DUH-DUH!!! moment so to speak. it didn't have to make sense.
and of course there is the old chestnut that these episode were only supposed to be viewed ONCE. there was a presumption that viewers would simply "forget" the actual progression of events over time and just accept new twists the writers came up with because they was no way to backtrack or cross-reference anything. it's a cynical viewpoint but true.