We were in Wales last October. We attended a practice of the Dolgellau Mens' Choir and after they did their practice, I asked if they would do Gwahoddiad. They did not sing the same chorus as we do in the US (which is the same as in Caneuon Fydd!). I would guess that they sang the same chorus as the one sung in the video linked above.
Sian, or anyone, can you give me the chorus that is sung in Wales, and any thoughts on why it differs from the one in Caneuon Fydd, the standard hymnal? It appears that the verses are the same, but I did not try to track this. Cerys sings the CF version, more or less, I think.

Our Welsh Church here (and most of Oregon and Washington) got snowed out for Christmas. But we're doing Lessons and Carols this Sunday, because you can't skip a Welsh Christmas.

Nadolig llawen i chi gyd, Chris in Portland (OR)

P.S. Is anyone re-thinking the global warming theory?