Okay, here's something you'll want to keep linked, because it's catalogued badly by Google.
The Dictionnaire de Noels et de Cantiques includes words and music for a tonload of French popular religious songs. It shows up on Google as Encyclopedie Theologique, because it's one volume of a series of religious reference works put out by Migne under that name.
There are a _lot_ of French hymnals from this period that don't include the tunes, so this is a Very Good Thing to have online. It also has several nice indexes at the back (title, subject, etc.), so that could be handy. Of course, it would probably be handier if we all lived in Quebec or Paris; but it's better to have a link to something and not use it, than not to have it when you want it.
And of course, there may also have been a lot of folk process. A hymn that was written in the late 1600-early 1700 range, and probably traveled all around the French colonies of the world, has plenty of time and space to morph the lyrics.
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