It's my understanding that the tune is originally Seychellois-based and taken up by the Quebecois/Cajun/et al communities. But having never heard the Seychellois version I can't swear to that. But according to http://ickmusic.com/2005/05/29/chez-seychelles/ a native knew the tune when she was a girl there. I also understand that Michael Doucet massaged the tune quite a bit. The B Part seems to be subject to much interpretation, in the versions I've heard, at least, but a particular favorite of mine is BigNick's version at http://www.youtube.com/watch?v=kFPv0Wrlqas/ I don't know if that's his B Part or if he got it elsewhere. All the B Parts I've heard don't quite fit the A Part (in my mind), though there's nothing bad about any of them. Maybe it's time for a trip to Seychelles for a little music research!