Hello Michelle ,
I have been using the chromatic bass part of my accordion for 3 to 4 years, I am currently on vacation and I do not have the possibility to scan the schematic of MY left keyboard, I say "MY" because I am not sure that there is only one configuration (the debate is open), but I will be back towards the end of the month, if you are still interested, I will send you a photocopy of the keyboard.
Hang on because at the beginning, it's quite confusing and it doesn't fit all by itself but when you play an Argentinian tango (for example), it has nothing to do with the traditional chords, it's as if you were "piloting" a bandoneon and there, you don't need to dance it to enjoy yourself, it's another thing...
I wish you a good evening.
Best wishes.
Daniel