I think I'm a bit more confused than I was before...sorry, clearly more of a novice than I thought I was...!
So, I have ordered the marriage certificate for my Mary Parker Docherty, because I needed that for my niece's family tree and it will also confirm her parents (I know I won't have their marriage date from it but I can get that later).
Am I now scrapping the idea that the John Docherty who married in 1911 to Elizabeth Parker the confectioner is my John Docherty? Or is that marriage right and he was born John Dougherty in 1880, but I've got the John and Elizabeth that I thought were his parents wrong?
I also found this headstone that I think belongs to my original John Docherty and Elizabeth Parker:
https://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=141884248Sorry!
I have another stumbling block on another branch of the tree, but I'll probably start a new thread on that...