I always thought Angelique's timeline went as follows:
1692 (as Miranda)- she then eventually died.
1795/1796- reincarnated and made a witch per Angelique's Descent.
1840
1968
1796
1897
1970
Angelique was making annual trips to check that Barnabas was still chained in his coffin, so in the original 1840 she saw the chains and then left town. The same goes for 1897.
I always thought that following 1897, there were two Angeliques in the 1968 period. While she was Cassandra at Collinwood, her present self was in New York as a model, eventually meeting Sky Rumson and marrying him. She clearly avoided Collinwood altogether in 1968 to avoid messing anything up.
At the point in 1897 when Quentin is saved from being killed, Barnabas makes a statement "David was never possessed". which would be the true case, as there is no ghost in the present time. But the writers forgot all about this by having present time characters still remember his ghost. By the summer 1970 haunting of Gerard/Daphne, everyone seems to have forgotten Quentin/Beth's haunting by not commenting on the similarites between the two.