Perhaps I'm missing something, but isn't there a HUGE continuity error with the death of Edith in 1840? Since she was the grandmother of Judith, Quinten, Edward, and Carl in 1897, her death in 1840 (before she and Garbriel had chilldren) would have prevented the four grandchildren from having been born. If Edward had not been born, there would have been no Daniel, no Roger, and no David. There also would have been no Elizabeth nor Carolyn. Thus the entire family that existed in 1966 would never have been born, so Vickie would never have taken the train to Collinsport for a job at Collinwood.
I won't even begin to discuss what Angelique/Valerie/Miranda's death in 1840 would have meant for the 1897 and 1968 time periods. Also, would Gregory Trask have existed in 1897 following the death of Lamar Trask in 1840/1841PT?
Needless to say, the events in 1840 certainly changed more than there being no Gerard's ghost in 1970.