I can just imagine the conversation in the Webley marketing department when they learned the boffins in the engineering dept had developed the bronze rings piston seal. "How can we present this as a 'target special' and sell a load more air pistols?", they asked (yes, I'm that cynical!).
I suppose the question is, did the Mk2 plus Mk1 sales represent an increase on the number of Mk1s that would have sold anyway? Hard to untangle.