Thanks Forfarian,
since I made my post, I have the the records on scotlandspeople and are inclined to think that as the couple were from different parishes, and Frances was from a non-conformist church which could not marry a couple without it first occurring in a Church of Scotland, that the marriage occurred first in Glasgow and then in the non-conformist Rutherglen Relief Church. The marriage date is the same on both records but is recorded with a later date in Rutherglen.
After discovering this information, I have come back and read your post which appears to correlate with my information, thanks.
I have researched as William Bulloch's birth dates have been variously given as 1816 and 1818. Only one birth in Glasgow is recorded as occurring in 1816 to the parents of James Bulloch and Christian Erskine.
I find it somewhat off-putting in researching a common used name like William Bulloch linked to a relative whose name is variously listed as Jane, Jean and Janet. I never really sure if I am dealing with the same person, sisters or members of different families.
Thanks for all your advice. The last 24 or so hours have been fruitful in adding one general generation of ancestors to one branch of the family tree. Most days, or weeks, are this productive, unfortunately.