Hi Sancti,
it's possible but I doubt it somehow. All the members of this family were in the Free Church of Scotland and rather strict although theymay not always have been that way.
It seems though as if there is a chunk of marriages missing between 1760 and 1820, either that or there was nobody there in that period named James Bryce or Jane Graham, which I find strange.
They are not the only ones doing a disappearing act either: I have a Sarah Todd, who married James Elder in Glasgow on 18th August 1846 and both the 1851 and 1861 Census records list her as being born in Dumfries in a place called Minihive or Moniaive and the date of birth is around 1823. Her death certificate shows her parents as Alexander Todd and Janet kerr, but again there are no records for the birth or the marriage.
So I guess I'm stuck with both these families.
Greenvalley