I have a printer with the CN642A in my office. Unfortunately it is incredibly dirty with ink, but I will nevertheless try to print test patterns with individual pins covered. The heads have a swash width of about 15mm. At 600dpi (is that the native resolution?) this would give us about 350 nozzles per color. One of the pins is likely a heat sensor.
I would like to have a breakout board made that connects all pads on the cartridge via pogo pins to a standard 0.1″ pin header. I did start a bit of work already in eagle and I will post files as soon as they become usable.