Plot hole: How did UNIT soldiers manage to get the TARDIS through an ordinary door into the Doctor's dorm in the research centre? The Doctor's labs in the various UNIT HQs had either double doors or a removable partition wall. The research centre is supposed to be an ordinary country house with single doors and solid walls. The TARDIS is larger than the average wardrobe and, unlike most modern wardrobes, doesn't come apart so it can be got through doorways. The TARDIS is known to be a "Type 40 capsule"...but there's never been any mention of the TARDIS being an IKEA-style "flat pack self-assembly" time machine...
The Daleks - S1-E2
Visible crew/equipment: Toward the end of episode one, when Ian is wondering where Barbara is, the shadow of a boom mic moves over the door behind him.
The Dalek Invasion of Earth - S2-E2
Other mistake: Ian has completely forgotten the distinctive shape of a Dalek. It's only when the Dalek starts speaking that Ian says to the Doctor, "that voice". Yet later when they are at the saucer, he talks to the Doctor about the new back of the Dalek having a disk on them now.
Destiny of the Daleks - S17-E1
Factual error: Davros comments that, between them, The Daleks are carrying half a megaton of explosives - in other words, roughly twenty-five times more explosive force than the Hiroshima or Nagasaki bombs. An explosion of that size should cause enormous destruction (vaporizing everything within roughly two kilometers), yet when the Doctor detonates them they explode with about as much power as a small stick of dynamite each.
Revealing mistake: In the end part of this story, in the large spider's den, the string supporting it is visible.
Revealing mistake: The Filer vs. Filer fight in the lab is very amusing, not only because of the several glimpses of the stuntman doubling for Filer, but also because of the way the "metal" railings around the set wobble as they slam into them.
The Invasion - S6-E3
Audio problem: The first victim of the hypnotic signal stops walking when he hears it, but the sound of his footsteps continues for several seconds afterwards.
Character mistake: The Doctor gets Jo to do some mathematics to distract her. At one point she says "49 x 2=88", when it actually equals 98, then she says that "adding 10 equals 108". (In other words, Jo (Katy Manning) fluffed her line, got one figure wrong, then went back to script...).
Plot hole: When the Doctor goes into the CET projection of Eden, to fight the Mandrells, he disappears into the bushes on the left-hand side of the screen. Cue much shaking of foliage, and Tom Baker's cries of 'ooh', 'aargh' and 'ouch'. The Doctor then reappears with his clothes all tattered and torn, due to his 'fight' with the Mandrells...but the the fact that there is not a mark (not even a scratch) on Tom Baker is something of a giveaway that all Tom Baker did was disappear behind some bushes and do a quick change into a tattered version of his costume.
Plot hole: Azmael doesn't recognise the regenerated Doctor (In the shape of Colin Baker) whereas on most other occasions other Time Lords do recognize each other through telepathy. This is odd behaviour by Azmael, considering that Azmael and the Doctor HAVE actually met before, and possibly more than once. (Azmael last met the Doctor in the Doctor's fourth incarnation, and was the best teacher the Doctor ever had. On that occasion, Azmael got drunk.).
Visible crew/equipment: When Romana brings the Tracer near the jewel cabinet in episode one, the wire powering the prop can be seen at the bottom of her hand.
Revealing mistake: The "crystal" tube holding Sarah wobbles whenever it is touched.
The Monster of Peladon - S11-E4
Revealing mistake: Eckersley - who supposedly knows the mines better than even the natives of Peladon - drags the queen through the same set twice, once each way.
Factual error: One of the characters in this story is called "Lord Ravensworth." Yet the story is set in 1813, and Sir Henry Liddell was not ennobled and raised to the Peerage to become Lord Ravensworth until 1821 (eight years later).
Other mistake: The Master says he wrote 5,000 words a week for 25 years and Zoe says "but that's over half a million words." Yes it is, to be exact, six and a half million words. (5,000 x 52 x 25 = 6,500,000).
Revealing mistake: In episode one, as the Doctor is repairing the buggy, one of the patrol runs on too soon, realises that he's come in ahead of his 'cue', and runs back.
Other mistake: The Cyber Leader is supposed to follow the Master's footsteps exactly in order to get across the chessboard. He doesn't. This cannot be classed as a character mistake because the Cyber Leader knew what was involved. I believe this mistake was caused by the actor not being able to see the chessboard through his helmet.
Revealing mistake: Watch really closely when Leela throws the knife at one of the robots. You can see the knife fall to the floor about a second after she throws it. Then, of course, the next shot shows the knife sticking out of the robot's chest. Guess Leela isn't quite as good a shot as we thought.
Revealing mistake: In episode three, when the root attacks The Daleks in the mining area, the string holding the root up can be seen.
Battlefield - S26-E1
Deliberate mistake: Look for the "creases" in the wall inside the TARDIS, which look as if the wall was just a sheet hung up behind the console. (In fact it actually WAS a sheet and not a "solid" wall - the TARDIS wall prop was apparently unusable due to water damage, due to poor storage between seasons. This also explains the lack of TARDIS interior scenes throughout the rest of season 26: it was not thought worth repairing the TARDIS set [or building a new one] when the show was in imminent danger of being cancelled after season 26).
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