A babe is born all of a may

Okay, granted, this folkloric, mediaeval Christmas song is too much to ask of a congregation. But it's sweet, and fun.

It does not argue for an unorthodox dating of Christmas: "may" here is a variant of "maid(en)", i.e. virgin.

The Oxford Book of Carols OBC cites manuscripts dating to the fifteenth century, which seems consonant with some of the phrasing (e.g. "The herdes heardyn" for "The shepherds heard"); the tune is from Bramley and Stainer, 1871, and is #116 in OBC and #27 in the Summit Choirbook (SCB).

I think I would go with the nuns' text (which they say they took from Bramley and Stainer) but perhaps with Martin Shaw's (OBC) arrangement.

The Hymns and Carols of Christmas has two archaic and one slightly modernized ('maid') versions.