Have you tried variable spelling of the name? Could be Gibbins, Gibbons, devon accents can change the spelling over time. Have you looked on National archives for the surname and parish, in case he was illigit, and his mother married a Gibbings? Or try a marriage of a William and Mary in the parish, to see what surnames come up. He could have been married in a different name, and then found out later that his name was incorrect, I have had that, fortunately with mine they had a child which was registered so I was able to work it the other way around, using the mothers name to find the marriage.