Hi Alan

1994, 95 and 96 were odd balls as GM was converting from OBD-I to OBD-II
Thus the CCMs were also odd as in 1997 GM went full bore OBD-II as EPA required
All changed as odd years used PCM and CCM where ECM used a E-prom to store engine calibration, pre 1994
ECM then was connect to CCM via low speed network as CCM is the commander of the network

Both exchange information via the network where common connection to both are via the ADLC under the dash

This means tools do connection to the ADLC and talk over the network, so yes the older Tech-1 was used by GM tech's to do updates, etc

If the CCM you have now is working OK for HVAC, seats, radio, etc I suggest solving this as I do for my customers is turn VATS OFF in the PCM tune and forget about finding someone who
can talk to the CCM as VATS could fail later on and your back to a problem again

Your better off as this way if the ign switch or key pellet goes bad or even VATs fails with it turned off in the PCM all that VATS functions are ignored.

Your 1996 uses a PCM, difference is it has flash memory and not a E-prom as ECM did.

I cannot recall but you might want to look to see if shunting certain pins of the ADLC is used causes PCM and CCM to resync the security seed