Though we subsequently learn that everything we thought had been the backstory of the past (which wasn't actually 1795 but somewhere around 1830) either wasn't the whole truth or indeed completely made up, so that's why for the purposes of the storylines from the point of the 1795/96 flashback onward we need to discount everything we were ever led to believe in Eps #1 through #365 as if we were never led to believe it (one of the major problems with retconning
). Plus, in 1897 Barnabas doesn't flat out say that when at the age of ten he saw Laura she was already married to Jeremiah.
He could have simply been referring to the first time he saw Laura at a point in the past before the marriage. For example, anyone could make a comment about something that was a part of their past life (in this case Jeremiah and Laura's marriage) and then also correlate it to something that took place ever further back in their life (Barnabas seeing Laura when he was ten) and it wouldn't mean both events were concurrent with one another. (Plus, at one point in 1897 Barnabas refers to Jeremiah as his cousin, which certainly was never the case, so...)