The fact that there is such an enormous amount of music in the world that it is impossible to know it all or collect it all. I am excited by what I don't know, it invigorates me and my passion for classical music to know that I have only heard a handful of pieces by Berio, none of Beethoven's late piano sonatas and nothing by Barraqué.
From what I know of your tastes in early music, I wouldn't hesitate to recommend some of Mozart's shorter liturgical works like Misericordias K222. Of course, I can't predict what you would like or wouldn't like, but I know that some people (like myself)