I would approach Labounsky's grading levels with some caution. Yes the very difficult pieces are very difficult, but beware of the E and VE designations. Even though she lists "La Nativité" and "Fugue" from Vol. 1 of Vingt-quatre Pièces as easy, they in fact are not. I think she would clarify these ratings by saying that an E rating doesn't mean you won't have to practice diligently, and - if it needs to be said - if your playing isn't concert level you should stay away from the D and VD pieces.