hey msbryk,
1840 is one of my favorite storylines, but there are definitely some inconsistencies that have left me scratching my head too. hope you enjoy your first viewing of it - i think it's really fun! and you're right - it is pretty to look at.
piggybacking onto what mb was saying above, it isn't ever stated what the ages of gabriel and edith's kids are - in fact, being "away at school", they could even be older than tad, imo. maybe the father of edith, quentin et al was almost university age?
edith getting killed in the 1840 storyline creates a paradox that many dark shadows fans have debated for years. i can't explain it either, except to say (somewhat cynically) that i'm sure the writers likely didn't care if anyone remembered edith from 1897, and certainly never dreamed we'd be sitting around, virtually, talking about why they did what they did forty years later. inconsistent, sloppy writing/continuity like this certainly isn't uncommon on television.
as for the leticia/pansy similarity - i'm pretty sure everyone just liked nancy barrett as that character, so they brought her back, albeit with a different name. perhaps leticia's meant to be an ancestor of pansy?
as to daniel supposedly having been the last of the collinses in 1795/6, i don't remember ever hearing that, but perhaps someone else here does. since we were later informed that the collins family came to maine in the 1690's, there were certainly enough generations between the 17th and 19th centuries for an offshoot line from which desmond's unnamed father sprang. plus, with the collins family being so...peculiar, i'm sure that even if they had said daniel was the last collins, there would've been some black sheep of the family in the 17th or 18th centuries that didn't make it into the official family history, who nobody acknowledged. yeah, that's fanwanking, but it could be used to explain any "cousin" showing up later on the show.