I may be mistaken, BUT I believe the cock of the lock on the BB gun has been either replaced or at least repaired. I say that because I was talking to Mark Silver about the engraving design on the lock, which is similar to the engraving on the Edward Marshall lock, however the engraving on the cocks of both of these locks has not survived.
Anyway I don't know if it's worth worrying too much about the cock in particular, since it may not be as originally built.