You are wrong; there are. Various pieces fall off throughout the shoot but the blaster started with all greebs mirrored. We know that one of the split plugs falls off the generally unseen side of the stock (what you are referring to) and we know that the connecting rod falls off the seen side as well as one of the molex connectors but people rarely replicate these pieces missing so I don't understand why they choose to miss off the split plug.
Split plug on both sides (falls off).
.
Missing connecting rod
Missing Molex (it would seem the connecting rod is missing here too).
So the blaster starts with two way symmetry apart from the MPP holes and Webley itself which sacrifices symmetry for the addition of the stock bracket although if one takes the left hand grip from a Mk VI revolver or the Webley 4" Flare gun it would fit (although then the bracket and stock would be missing obviously).