Basically, the RMS modules are more or less functionally identical. They all operate on the same principle of accelerated RMS detection (averaging the log). There's not a lot of difference to be expected operationally between the very oldest potted modules and the newest monolithics.
Almost the same could be said for the VCA's except there were three main functional variants:
6.02mV/dB, which is the natural control law for the core, and
5V/100dB or 10V/100dB, both obtained by a voltage divider in the control port
It is relatively easy to determine what type by measuring the control voltage under working conditions. The first type will measure at a few hundred mV max, when the others will show a few volts.
There's a whole lot of difference between potted VCA's: the original one operated in class B, then some in class AB. The THAT corp website traces the history of VCA's and their variants, but it is quite difficult to know which is what. It seems that a number of ECO's have not been very well documented, or lost through the numerous changes of ownership/location.