This episode was actually mainly in tune to a regular soap opera storyline as in the first year of DS.  They should have continued the Paul Stoddard storyline in this manner separate from Leviathan.

I like spoilers no matter how much is written.

[spoiler]Natalie was probably released from the spell once Barnabas leaves 1796 back to his former self as I think Millicent was when he arrived the last time from 1968.  I said before I think this is a fantasy 1796 conjured by the Leviathans to capture Barnabas, the rest was window dressing.  Perhaps the real Kitty never left London at all.  Any "correspondence" to Edward wouldn't have been from the real Kitty either.
[/spoiler]

I suppose the Cannery was still there in 1840.

Despite all the changes made, it appears to me that the Collins family we leave behind in 1897 isn't as different as they were in the original timeline.  Barnabas, Angelique, & Quentin are gone for good, Beth is dead.  Jamison never forgave Quentin.  The villains are all dealt with and gone as well.  Magda & Charity are still there but they probably were originally as well, though Judith may have eventually gotten to reform Charity somewhat like her old self.  1897 Barnabas is unknowingly chained in the coffin in the secret room as all connections to him are gone (I believe when 1968 body Barnabas went back to 1897, his 1897 self had to be returned to where it was taken from, the I Ching restoring the room back as it was.)

I still see the same setup for 1966 as the core of the family is basically the same.

This was dealt with in the movie "Time After Time", when H.G. Wells arrives in 1979 San Francisco from 1890's London  with 19th century money.  He goes to a Bank of England (?) and the teller (soon to be GF) said there wasn't any problem with transferring the currency even though it was many years old.

Actually, that Quentin with the bright suit and yellow shirt may not exist anymore as Petofi in Quentin's body instead may have been in a trance from 1897-1969 and that's why he wears the 19th century clothing.

I think Petofi may have inadvertently changed future history as now that he is in Quentin's body, there never was an active, living Quentin for all those years.

[spoiler]First time watchers would never guess that 1897 is actually winding down at this point.[/spoiler]