Earthshock - S19-E6
Revealing mistake: When the Cybermen break through to the bridge, they brush against the door and it bends as if made of cardboard. It was supposed to be made of reinforced steel. (01:09:10)
Earthshock - S19-E6
Revealing mistake: During the "cliffhanger ending" at the end of episode 3, it's blatantly obvious that the three columns of advancing Cybermen are merely mirror images of each other. The head of each column has black head bars indicating leadership, and is holding his gun in exactly the same position.
Earthshock - S19-E6
Revealing mistake: When Lieutenant Scott kills the second Cyberman on the bridge, he starts falling down way too early.
Earthshock - S19-E6
Revealing mistake: The "dead" crewmembers at the end of episode two can be seen breathing.
Earthshock - S19-E6
Revealing mistake: Just before the Cyberman fires on the console, you can see Adric trying to keep as far away from it as possible before it explodes. (01:35:05)
Answer: TARDISes are generally available for properly authorised use on Gallifrey; they're not usually assigned to a particular Timelord on a long-term basis. The Doctor stole his when he left his homeworld.
Tailkinker ★