Thanks andyjh,
I understand what you are saying. I finally figured out what was throwing me. The CC display indicates a RANGE of cc values which will switch to a particular cell. I assumed I would get one value per row/column - whichever I was switching. So, when I see the two numbers flanking a dot (corresponding to a matrix position), it means any cc value inside that range will switch to that matrix position. It seems simple now but somehow it isn't something that naturally occurred to me. I was expecting ONE cc value per row or column.
RE the advantage of using cc instead of key switching: You don't have to hide score notes which have nothing to do with the actual music pitches of the composition.