Surely there must be more folk interested in the story of carols

Well, yes --- in my case very interested but pig-ignorant! My two-pennyworth on medieval carols being that the standard form in England was refrain-verse-refrain-verse-refrain (etc .... quite long, some of them!), the verses having four lines and the refrain two. Oh, and the tune is 'at the bottom', in the tenor (hence the name), with the contra-tenor singing ornamental wiggly bits above. Does anyone know if this English form derives directly from the requirements of the dance-form?

And was there any particular reason why, when the refrains developed from two- to three-part writing, the verses tended to remain for two voices only? Going off at a related tangent, I notice that the normal 'third' part in the refrain of There is no rose of such virtue is actually an editorial addition by the late Professor John Stevens. I haven't gathered whether he was trying to reconstruct something for which specific evidence exists, or was simply making an academic point by writing in what he thought should be done with the song. Anyone know?