as that "barmy" caretaker told us in 1967
ad nauseum "
L. Murdoch Stockbridge died by fire..."in the original telling of Laura's story she married into the Stockbridge and Radcliff families in her previous Collinsport incarnations. her subsequent inclusion in 1795 and 1897 was a complete rewrite.
it was also a completely unnecessary rewrite. having Laura married to Jeremiah in the 18th century not only threw continuity out of whack but didn't add anything to the overall mythology. if they wanted to retroactively include in that period she could have come to Collinwood as the wife of another relation. there was no dramatic purpose for her to be married to Jeremiah. it was sloppy.
as for her marrying into the family in the 19th century who knows??? they probably thought the show was so poorly rated in 66/early 67 few viewers would have even known she had previously been part of the story.
to say nothing of the fact the Pheonix's 100 year cycle gets totally thrown off with each appearance.