Possible keys of play on "G" accordion? G,A,_,C,D
Primary Keys----"G"(mostly push) and "D"(mostly pull, or playing in the 5th)
Secondary Keys--"A"(blues key) and "C"(backside key).
The only key that a "C" accordion cannot match up "well" against what a "G" accordion can do is the key of "A". "A" happens to be the rarely played blues key of the "G" accordion. So not a really big deal.
Or, one could do like they used to do at Savoy's Jam when someone broke out with a "D" accordion. The jam continued on, but all of the beginner accordion players would not play along with their "C" accordions due to their own ignorance and the unaccommodating ignorance of the "D" accordion player.
Possible keys of play on "D" accordion D,E,_,G,A.
The "D" player could have made the "C" players aware of the "C" accordion's blues key of (D). The "D" player could have also got some practice playing the dreaded backside of that "D" accordion which would have been the key of "G" which would have been an easy dream for the "C" players.
Melo, you are absolutely correct sir.
I think that learning all of the "positions" on that accordion should only take a few years if you are aware of them right at the start, and chase after and/or are shown or told the correct methods of actually playing them. I call them "keys" now. "Positions" is a confusing term and it scares young Cajun or beginner Cajun accordion players into doubting themselves. "Positions" is too fancy a term. It implies difficulty. "KEYS" implies "ACCESS"!
I've always found that the most important thing is to the learn all the notes of the buttons. That will give you the ultimate freedom of just knowing where stuff is at. Put a little music theory (very basic) on top of that, and I think anyone can play in any key. Obviously, with increasing limitations depending the key being played in relative to the base key of the accordion (some key-to-accordion match ups may limit you to only 1 or 2 notes, and maybe not even the root note of the tune's key). Considering some of these extreme limitations, some would argue that it isn't even worth playing if the key-to-accordion match up isn't in the norm, but if you know what notes the buttons are you at least don't have to put your accordion down when someone switches things up on you.