I found this interesting tidbit in the
2ch link Revoc posted in another thread.
Somebody asked in
IGA's blog, about X Chronicle (PSP remake OST) if stage 4 was "Slash" or "Op.13". IGA answers "Slash" is correct as he asked the composer so the OST was incorrect.
So maybe the sound test was wrong and the current notes aren't right?
EDIT: Metal Yuhki seems to imply from the liner notes he did arranges like 04, 06, 08 and 17