By the time of the IIIa, most of the proprietary film rating systems were history, the IIIa appears to have only come in either DIN or ASA. But both systems were young and not fully adopted yet when the Contax III was released, so it is not unlikely that were offered with Weston, Scheiner or BSI engraved knobs in some markets.
Still, the combination of the very US (the British empire used BSI in the same period) Weston system with the very non-US metric distance scale is odd - did Central and/or South America use Weston?
Another idea: What do the sensitivity scale values read? The Weston system preceded ASA and used the same scale, that is, the familiar 25,50,100,200,400 sequence, while GOST used a slightly odd 32,65,130,250,500 series - even if some faker manipulated the ГОСТ or GOST (some early Ukrainian and many export models had latin engravings) into a WEST, he could hardly deal with the knob scale the same way.