Goodness, you really do find puzzles :-)
Does this mean Robertina has lied about her home address when she got married and if so why?
Okay so Jeremiah Colvin and Jane Eunson were both from Shetland and were married in Lerwick in 1894.
https://www.bayanne.info/Shetland/getperson.php?personID=I93466&tree=ID1 At some stage between 1894 and 1900 they moved to South Shields, there was a child James Robert born and died, bless him, in Q2 1900, South Shields. So, unless you have something that would link either Eunson or Colvin to your tree, they are unlikely to be relatives. There were lots of ex-pat Shetlanders in the North East (including mine).
Many possibilities as to why she gave that address, maybe she knew them and stayed a little while before the marriage to comply with the residence requirement for banns? Maybe she boarded with them while working in South Shields? Maybe in between census years William temporarily was living and working in South Shields and she did the same to be nearer to him? I wouldn't expect Robertina to be on an electoral roll at that time anyway as she would almost certainly not have qualified to vote.
Why has Margaret Ann Moore changed who her father was?That's a really difficult one, there is evidence (census returns etc) to show that its likely to be the same woman on both marriages.
Do the ages on both marriage records match with what you'd expect? - or do they just have the old standby of 'of full age'. Any clues with the witnesses names? Any Thompsons on either record?
I'm not finding a marriage for Margaret (Ann) Thomson to a groom called Moor(e) in the right time frame for her to be a widow by 1855 but that in itself isn't conclusive (especially as I failed to find a death for James Denham).
Its not beyond the realms of possibility that an error was made in the register (the register details would have been written in advance ready for signing so its 'possible' whoever did that got mixed up and put the wrong father's name down) but I checked the registrars site and there were no Thompsons married in September in St Hilda's so that's a real long shot.
or maybe, just maybe (I do know a case where it happened) she'd discovered that the man she thought was her Dad, wasn't. Quite how you'd prove any of the possible scenarios I am not sure.
Will have a think and post back if I come up with any straws to be clutched.
Oh and question your parents exhaustively about any other certs/documents etc etc they may have squirrelled away ! :-)
A few years ago I asked Pa in law (after scanning the myriad of certificates, grave deeds etc etc they had) if I could have his permission to apply for a copy his RN service record. Oh said he, that's in the sideboard in the dining room. When I enquired as to why he hadn't mentioned it he replied that he didn't think anyone would be interested! What is gold dust to a researcher is just an old piece of paper to people who don't do this stuff :-)
Boo