As a player of an 8 bass button accordion I'm intigued by all the bass buttons on a 120 bass accordion. I understand the 48 and 72 varieties whereby each row of bass buttons is the counter bass note, bass note, major chord, minor chord etc. But what are the extra buttons for outside this central matrix of 12 x 7?

I found a site but it was in German so I couldn't make much sense of it but it wasn't an extension, up or down, of the central system?

Also the counter bass buttons: I presume they are there so that, for example, when playing in C major the bass notes C, E and G are close together. Is this correct?