I'm sure this answer is somewhere, but I cannot find it. I also don't really know what math there is to do to figure it out. How many different combinations are there with just the 12 buttons?
On each row you have four options (L,M,R,0) so 4*4*4*4=256 chords... except that 0000 is not possible, so it's 255 real chords.
One button chords 12Two buttons chords 54Three buttons chords 108Four buttons chords 81