A couple of other extreme-technique recorder pieces to look for: Luciano Berio's "Gesti" and Maki Ishii's "Black Intention". Eve O'Kelly's book "The Recorder Today" (1990) gives an idea of what had been done 20 years ago, with a list of 400 compositions.

Most books on recorder technique will tell you how to go a whole octave higher than WAV's upper limit. Two octaves and a minor third is straightforward, beyond that every instrument acts differently.