I'm learning to play chromatic button accordion (C system) and my main reference is the Galliano method book (Complete Accordion Method).
This book contains reference material for how to play scales. However, it uses the first three rows only, and sometimes I find the fingering awkward. For example, the ascending C major scale goes from F in the third row with the fourth finger to G in the second row with the second finger - essentially you have to move your whole hand and it's not smooth.
I found that playing G with my thumb followed by A in the fourth row with my third finger is smoother and faster, so I've switched to that.
Do other people play major scales like this? Is there a lot of variation among CBA players? I originally learned music on piano where how to play scales is standardized.