Hi Dougs 123,
I have no idea if that G stands for Glassary. Maybe Monica will know.
I found the marriage of Mary Darroch on
www.scotlandspeople.gov.uk, using my Miss Marple skills
I just keyed her name into the search and looked for a marriage in Argyll between the years of Duncan's birth and the next Census. When I got a hit I started going through the alphabet looking for a natch to the groom's name. Sounds really time consuming
but to be honest it didn't take me long.
Then I searched on FamilySearch for Mary Dawson in Argyll on 1881. Then I looked for a Duncan Dawson, making the assumption that Duncan Darroch took his stepfather's name when the couple married. Maybe Duncan never liked this arrangement
. Because from the info found by Monica it looks like he changed by 1891 to Campbell and you yourself have proof of that with the 1901 and his marriage.
It wasn't unusual for illegitimate children at the time to be known by their father's surname even though it was not on the birth certificate. So Campbell may well have been Duncan's biological father's name and Archibald could well have been his first name. Then again it may have been a name Duncan made up to look "respectable" when he married. Did he call a son Archibald?
Do you have Duncan's death cert? Does that give parents names (although of course that info is only as good as the knowledge of the person who provided it)?
But to conclude ...yes I think Duncan Darroch became Duncan Dawson became Duncan Campbell.
Maybe Mary's death in 1923 would be worth looking at, see who registered it and it will give you her parents names.
Looby