With reference to the tune Caerlleon from the Calvinistic Methodist Hymn & Tune book. An article in Y Cerddor Cymraeg (Medi 1864) states that the melody showed up in "Flora Opera", (1729), "Cobblers' Opera"(1729)and "Opera Achilles"(1733)and was known in England as "Come open the door, Sweet Betty". This information I got from "Tonau a'u hawduron" by Huw Williams(Llyfrfa'r MC, Caernarfon. 1967)