"early" vs "later" prodigy

Hi, I can’t seem to figure out how to tell if I have an early or later model of Moog prodigy? I am need of a replacement key. Thanks!

The parts list of the service manual does not list separate partnumbers of the keys for different serial numbers. But I assume, that @Sam might know it better.

Basically there were three revisions. Up to serial no 2000, up to 4160 and above 4160. The latest revision has labeled CV/Gate in and out sockets at the rear panel. Older models may have those sockets, but are missing the label printing on the panel.