Rhapsodie sur des Noëls

I treated myself to the Oloron sampleset recently, so this is my first recording on it, characterised more by enthusiasm than accuracy, but never mind.

I think this is a great piece, possibly not up with Gigout's Big Three (the Toccata, the Scherzo and the Grand Chœur Dialogué), but close. It's very rarely played in recitals in my experience, possibly because it is rather seasonal.

I've never been able to identify for certain all the carols involved. Adeste Fideles is obvious, and the Gloria from "Les anges dans nos campagnes," but the main tune which it starts with is sort of "C'était la veille de Noël" but I'm not entirely sure. Perhaps our francophone colleagues can enlighten me?