Factual error: The Doctor postulates that ammonium sulphide will poison The Ice Warriors because the Martian atmosphere is composed mainly of nitrogen. However, it is the EARTH's atmosphere that is mainly nitrogen (78%) whereas Mars' atmosphere is 95.3% carbon dioxide.
Factual error: It is stated that removing all the plants caused carbon dioxide levels to drop. But plants absorb carbon dioxide, so removing them would create an increase.
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