Sorry I didn't warn about my spoiler.
Nelson... since the very point of their going back in time is to change the present, certain events and storylines will be cancelled out, unavoidably. Much of what happened earlier in DS never happened by the time DS ended. Yes, 1840 cancels out many things, but so did 1897. The biggest, most glaring error, something that threw a monkey wrench into things in a totally unnecessary way, was Barnabas's
SPOILER
...refusal to get back into the coffin, physically.... twice. So BC was never there for Willie to set free in 1967.