Just a thought: we know the Mk V had an extra machine-gun position between the rear horns; does anyone know if a gun was fitted in the mount permanently or only when required? The V had two extra crew members available, so was the rear gun permanently manned? Did the V carry a spare mg, as the earlier Marks did? If so, would it be used in the rear mount if needed?
There's probably a more economical way of putting the above questions, but it eludes me at the moment.
So, obviously, the next question is: what was the situation in the V*? That had four more mg mounts than the V.