https://cy.wikipedia.org/wiki/Gwenafwy
Welsh Wikipedia states Gwenabwy and Gwenafwy refers to the same Welsh saint (who also seems to be referred to as St Wenappa, I assume that's a Latinisation), so it's possible they are all different ways of writing the same name. I don't know anything about mutation in Welsh consonants, so I can't speculate why the B is there. But I hope the possible link between Gwenafwy and Gwenabwy is useful to you.
This message was edited 6/18/2016, 11:43 AM