Mission to the Unknown - S3-E2
Trivia: William Hartnell appears in the credits at the end of this Doctor Who story... despite the fact that he did not actually appear in this episode at any stage. He had a contract that he would be in the credits for all episodes, which ended after he left the show in "The Tenth Planet." Though he wasn't shown, he had to be credited.
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