If you look again at the other discussion I linked to earlier, you'll see that W D Watson, who heard the song from Thomas Beard and passed it on to the Rev G H Doble, was the very same person who translated Mr Beard's verses into Cornish, and added another for good measure.

He adopted his Bardic name, Tyrvab ('Son of the Soil'; he was head gardener for the Corporation at Penzance), on his initiation into the Gorsedd in 1928; Doble was initiated at the same time, as 'Gwas Gwendron'.

The OBC doesn't make the connection and, since the editors refer merely to 'a version in Cornish ... with a fourth stanza', it isn't surprising that many people (Keith, for instance, at the beginning of this thread) have assumed that the original song must have been in Cornish. That is why I described the OBC note as imprecisely-worded. The editors do say that they 'owe the carol to the kindness of the Rev G H Doble', so presumably he provided them with it. There appears to be no record of when Mr Beard sang it, but some time during the 1920s would probably not be too far off the mark.

So far as the reputed C18 broadside of 'The Holly and the Ivy' is concerned, that is quoted in Sylvester's 'Garland of Christmas Carols' (1861), which can be seen at the Internet Archive: http://www.archive.org/stream/garlandofchristm00hottrich

It varies hardly at all from C19 broadsides, several of which can be seen at the Bodleian website.