I can't speak for all accordians, but the chords at the left-hands of piano-accordian players are arranged in circles of fifths. F is below C is below G is belo

I can't speak for all accordians, but the chords at the left-hands of piano-accordian players are arranged in circles of fifths. F is below C is below G is below D ... As a result, buttons for all the (non-chromatic) intervals are within 2 buttons of the tonic ... for every tonic. Once you've got the pattern, it's the same for every key, no matter how remote.