Charlie,
I don't know anything about cajun/zydeco accordions, but look at the following link ...

The wording in the description of this Hohner model leads me to think that this box is available in 2 different sets of keys, each box playing in 3 keys.

http://www.savoymusiccenter.com/zydeco_hohner_corona.html

They are probably saying that the 1 model is available in keys of G, C, F
and the other model is available in F, Bb, Eb.

[This message has been edited by MrEd (edited 02-01-2006).]