Tuning is a very dark science, and with one row accordions, it's really a matter of what version of out of tune do you like best. We've mostly simplified it in Cajun music to a somewhat standard style, at least when dry. The one debatable topic is whether to sharpen the 4ths or not. Some do, some don't. I didn't used to, now I sharpen the 4ths about 10 cents to start.
The one area I'd like to experiment with is what Jeff is calling dedic tuning. I've done one that way. I'm not a fan of wet tuning for cajun music, but I'd like to experiment more with this. Experimenting with tuning is not very appealing in the manner that you have to remove metal each time you tune a reed, well, that and the fact that I'm getting lazy in my old age.
"So, in a nutshell, DEDIC is LM+M-H as is common on Quebec boxes?"
Usually designated as L M- M+ H
It used to be more popular. As of late in Quebec one M row at "A" 440 then the M+ row.
If you see a description "equal tempered tuning" usually means no dedic.
I have a Quebec made box on its way.. when it gets here I'll see if it's dedic. About 10 days.
Consider this.. With dedic tuning if you want to play with only one M reed you are out of tune with every one else.
Often you will see Quebec boxes with non functional stops or only the L and H have working stops or no stops at all.. or often 2 reed boxes with fixed or no stops. These could be dedic as the idea is that MM are working all the time.
If you close off either of the M reeds you are out of tune with every one and yourself.