Hurley's numbers have their own blog.
My theory is that they are the opus numbers of various pivotal works by Schoenberg: Verklärte Nacht, the Six Orchestral Songs (4+8=12), The Book of Hanging Gardens (15 songs), the Five Pieces for Orchestra, the Five Klavierstücke (finished in 1923), and the Piano Concerto (written in 1942).
Related: my post on Lost and Alias composer Michael Giacchino; Adam Baer's LA Times profile of Giacchino.
