Most people think of time as linear... Time on a line. There is a past, a present, a future. I think, for the purposes a fictional show like DS, we should think of time as circular.
We do not travel back and forth between times and dimensions. So, we look at time from our perspective... linear.
:- If you think of time as a circular happening, you can understand the some of the confusing storylines on DS. Each little disturbance may create a different chain of events...
I believe this is explained on the show.
So, the fact that Quentin has a Time Staircase in the 1840s, and Barnabas & Co are engaging in all kinds of timeslips, means anything can happen. I think you have to take the characters you are with, and go from there.
First, remember 1967? When Barnabas got out of the coffin, he didn't look at Vicki and remember her from 1795. She did not go to 1795 yet. He didn't remember Julia saw him briefly in 1840. That, also, did not happen.
So, you follow the characters you are with. This brings us to 1840. This thread is debating: Is the ghost in 1970 Gerard OR Judah?
Well, I say it's Gerard... because, when the ghost is haunting Collinwood in the future, Julia hasn't gone to the past yet. However, and this is a big HOWEVER, it is very clear that Judah is behind the ghost of Gerard (and the other ghosts) haunting Collinwood.
Judah's plan is to destroy, and take over the Collins Family as revenge for 1692. So, there is a chain of events...
Judah is behind the chain of events which includes Roxanne, and he lures Julia and Barnabas back. Then, he uses Julia to achieve his goals. If he were to have acomplished his goals, there would be no ghosts in 1970 (or, 1995). Why? Because, Collinwood would have been his (as Gerard).
That doesn't mean things might have been rosy all the way for Judah... as far as this storyline went, we get back to the future, briefly, to see all seems peaceful. There are no ghosts, we assume.
There could be a ghost of Gerard (Ivan), or a ghost of Gerard (Judah). We're led to believe the best resolution -- ghosts of neither. Just remember, time on DS is circular, not linear! --wes