Clone Cadets - S3-E1
Continuity mistake: During the first training test, when Fives and Cutup have an exchange where the former tells the latter to flank right and gets a bad pun in response, Cutup is wearing Echo's practice armour (with a number 3 on it) instead of his own, which is marked with a 4. (00:10:38)
Continuity mistake: When Anakin and Padmé are walking towards her ship while discussing the situation, as happens with surprising frequency, Rex, walking behind them, is missing his kama (the kilt). (00:04:35)
Continuity mistake: When Ahsoka suggests that Chairman Papanoida's daughters might be being held on the Trade Federation ship blockading Pantora, she refers to it as a planet. "Trespass" established that Pantora is a moon. (00:06:47)
Continuity mistake: When Baron Papanoida walks into Jabba's court, his half-cape is missing. (00:10:24)
Continuity mistake: The intro states Aurra Sing is presumed dead on Florrum by the Jedi, but the Aurebesh writing in the archives states she was 'last seen on Coruscant'. Impossible. Perhaps the archives are incomplete? (00:03:33)
Continuity mistake: While training Savage, Dooku uses the Force to levitate a number of stone obelisks. While he's doing that, there's a closeup of Savage where an obelisk that is shown floating in the preceding and successive shots is visible behind him not floating. (00:03:36)
Continuity mistake: When the possessed Ahsoka declares that Anakin will be forced to kill her and Force-pulls one of her lightsabers into her right hand, said hand changes positions between the wide shot and the following close-up. (00:12:28)
The Citadel - S3-E18
Continuity mistake: When Ahsoka asks Master Plo if she can speak with him, her Padawan braid (the beaded chain hanging on the back of her head below her right horn) is missing. (00:04:05)
The Citadel - S3-E18
Continuity mistake: Just after Ahsoka says "clear" when they're sneaking around the prison, her Padawan braid is missing again. (00:13:40)
The Citadel - S3-E18
Continuity mistake: When the commando droids enter the cell where Piell's officers were being held, the damage on the door from Anakin stabbing a commando droid with his lightsaber through it is gone. (00:19:20)
Continuity mistake: After Obi-Wan's group has abseiled down the wall of the prison, two of the clone troopers in armour are carrying Separatist blasters instead of the Republic-issue blasters they had before and after. (00:09:38)
Continuity mistake: Besides Obi-Wan, Even Piell and Commander Cody, the exact number of people in Obi-Wan's group keeps changing.
Continuity mistake: When Ahsoka is boarding the rescue gunship, her normally green lightsaber has a blue blade. (00:18:00)
Continuity mistake: R2's squad of battle droids has three members. Yet in the climactic fighting of the previous episode, one of the droids was shown getting destroyed.
Continuity mistake: When Ahsoka takes cover in the trees after the Trandoshan ship opens fire, her Padawan braid is missing. (00:07:05)
Continuity mistake: When Count Dooku is speaking to Riff Tamson via hologram, the clasp of Dooku's cloak is missing in one shot. (00:00:57)
Continuity mistake: When Tamson is mocking Lee-Char about asking Nossor Ri for help, Ahsoka has her lightsabers on her belt even though she was disarmed earlier when she and Lee-Char were captured. (00:13:16)
Nomad Droids - S4-E6
Continuity mistake: During the incinerator scene, there are two RA-7 protocol droids seen. When the first one attempts to run from the incinerator, the one behind it has vanished, only to reappear in the next scene. (00:20:24)
Nomad Droids - S4-E6
Continuity mistake: At the end, when R2-D2 and C-3PO are reunited with Republic forces, Master Plo asks Commander Wolffe if he knows these droids. However, Plo previously encountered R2 in both "Rising Malevolence" and "R2 Come Home" (the latter episode having the same error).
Continuity mistake: Pong Krell's goatee is missing during the conversation he has with Rex during the march, most noticeably when he says "CT-7567, are you reading me?" (00:13:25)
Answer: Dooku never accepted Ventress as his apprentice, as far as I know; he just kept her as his devoted personal assassin. In Phantom Menace, it is stated that there can be only two Sith at a time, to prevent a power struggle in the lower ranks. To accept Ventress as an apprentice, Dooku would have violated that rule.