Could be nephew and being remembered as a brother perhaps! I've kept it in my notes as a thought. I've looked at nearly all birth records for Sarah Monaghan around the mentioned years and only the 18th Nov 1919 has a father of William. There is one record from 1922 which would match the year on her marriage certificate (23 in 1945) but oppose the 18 Nov 1919 on her death record, unsure if this could be a mistype up of '1922'. Unfortunately there's no certificate for the birth record so I can't see but it's for a 'Sarah Duffy Monaghan' in 1922 Ardoch. Which I believe is near Glasgow and my Grandma had mentioned a possibility of somewhere near there, but again it was a very long time ago and she wasn't certain.
Sarah Duffy Monaghan, mother's surname McChord, died in Falkirk in 1996 aged 74, so I think you can safely rule her out.
There is a certificate, but it's less than 100 years ago so it's not available online, and at the moment you can't order later certificates because Scotland's People is closed because of the coronavirus pandemic. It is not likely that 1922 on the certificate is wrong because records were collected annually. Far more likely that the age on her marriage certificate is wrong - she could be embroidering the truth, or the Registrar might have misread it or made a mistake.
Ardoch is not exactly 'near' Glasgow - it's almost 70 miles north-east, between Stirling and Perth.
