Here's some footage of a Portguese virtuosa, Eugenia Lima, being featured on a French TV show hosted by Jacqueline Huet, a French actress turned TV presenter.
Eugenia was still playing professionally until she died three years ago at the age of 88. If you watch her right hand you'll see her playing trills with her first and second fingers only, which was the way most of them did it in those days. The thumb was generally only used on the outer row of buttons, and the old teachers would not allow habitual use of the right thumb which they considered to be "cheating". Very few players ever bothered with the inside 5th row, and often had instruments with only 4 rows. In case you're wondering about her left hand they play 3x3 bass in Portugal, the same as in France.
Sorry if the tunes are not to your taste, but I posted the clip so that you could see her hands in action. The first one may be familiar to some of you as "April in Portugal", but it is actually a folk tune named "Coimbra" in Portugal. The second one is a corridinho, a folk style from the Algarve.
CBA is the most common type of accordion in Portugal, although the PA is more popular in Madeira and The Azores.