Continuity mistake: In Episode 1, the TARDIS crew pass out from the change in pressure as they descend into the Earth. However, at the end of episode four, they climb out on foot and suffer no ill effects.
Factual error: In Episode 3, Zarof fires a gun. The muzzle is seen and a sound is heard but the gun doesn't move and there's no smoke or bullet, no flash or anything at all. (00:23:05)
Answer: In 'The Five Doctors', three separate Cyberleaders are definitely used. So it's likely that Cyberleaders are like unit commanders, of which a fair-sized army might have several.
Daria Sigma