Plot hole: Jo is surprisingly skeptical about the TARDIS being able to move, considering she saw it dematerialise in the last episode.
Factual error: The calendar which shows the date to be Monday, 2nd March, 2472, is two days out. 2nd March 2472 will be a Wednesday. And who made the calendar if the colonists left Earth over a year earlier?
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