I have a question about the notation in a certain score. In Durand's edition of Ravel's La Valse, scattered throughout the piece are third staffs above the standard two. These aren't normal three staff sections, that are connected by a bracket, but rather separate things. My first thought was that they are an ossia of sorts. However, they are labelled differently throughout the piece, one section might have "quartor" above it, another might have "Fl.", and there are many other labellings. I've tried listening to recordings, but can't always tell exactly what the pianist is doing, it seems almost as if he sort of mixes them up. If any of you have any ideas about what these things are, imput would certainly be appreciated.
Topic: notation question