Most of the examples of "lots of chords" songs are the type that play one pattern all the way around the circle of fifths.
This got me to thinking - always dangerous. Just how many chords could a person use, WITHOUT resorting to modern atonal effects or extreme modulations, and without ever having any chain of fifths longer than vi-ii-V-I? Could I still use a button from all 12 columns of the Stradella bass?
Challenge accepted!
Attached is "Sonatina in D Minor," a left-hand torture device for your listening pleasure.
Sheet music:
PDF link
Computer-generated sound file:
MP3 link
It's a short classical-sonata-form piece. Any one passage should sound like could have been lifted from, say, a Haydn string quartet or piano sonata (though the overall effect is more 19th century.) Modulations only to closely related keys (G minor, A minor, Bb major, F major, C major), even in the development.
The final score: 28 chord buttons, 11 fundamental basses, and 8 counterbasses, including at least one chord button and at least one bass in each of the 12 columns. Buttons used highlighted in black below:
It is admittedly "not very accordion-istic;" it's written more the way you'd write for an organist, who is happy to play any two chords in succession and cares a lot about the voice-leading in the inner voices and bass line. And it uses chord buttons in a lot of places where it makes more sense to give one or two extra notes to the right hand and omit the button.
But the point was more to illustrate how many chord buttons COULD be used, if you cared only about the notes and not about making the player's life easy.