Earthshock - S19-E6
Continuity mistake: The hole that the Cybermen make in the door increases in size just before they step through it. (01:09:10)
Earthshock - S19-E6
Continuity mistake: In episode four, as they approach the TARDIS, the female member of the remaining troopers is grabbed and doesn't make it inside. But when the troopers do get inside the TARDIS, it's a man that's missing.
Castrovalva - S19-E1
Continuity mistake: The Doctor's shoes are different at the beginning of this story compared to the ones at the end of the last story.
Earthshock - S19-E6
Continuity mistake: The mouth panel of the Cybermen costumes was originally intended to be a clear perspex panel. During filming, it was felt that this showed too much of the actor inside the Cyberman costumes. So a decision was taking - mid way though filming - to paint over the 'clear' panel with silver paint. However, this does result in the mouth panels of every Cyberman alternating from 'clear' to 'silver' from shot to shot.
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