Continuity mistake: The clone troopers accompanying Jar Jar and Senator Kharrus are members of the Coruscant Guard and all have the unit's red armour markings. But in the middle of the sequence where the shuttle comes under attack, as Jar Jar is flung down the hallway, the troopers sitting across from Kharrus and Commander Stone have unmarked white armour. (00:04:33)
Continuity mistake: When Obi-Wan and Anakin snap "YES!" in response to Dooku's question, Obi-Wan's hands, cuffed together with a pair of handcuffs linked by an electrified cable, have somehow moved so the cable on his waist chain is inside the circle of his arms, despite that not being the case when he came to inside the cell earlier in the scene. (00:01:36)
Continuity mistake: At the beginning of the fight with the assassin droids, Anakin cuts off the right arm of the one Ahsoka ends up fighting. Yet during the fight, just before she says "Get back, ya pistonhead", the droid briefly has both arms. (00:12:10)
Continuity mistake: Before the clones retake the base, they have just enough blasters between them for all five of them to wield one each. When Rex is dealing with the commando droid captain, his left holster still has a pistol in it even though he loaned his other pistol to Cody. (00:14:00)
Continuity mistake: Wolffe, Sinker and Boost are shown boarding the escape pod twice: first from inside of it and then in the next shot from the pod bay running past Master Plo. (00:03:35)
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: Chopper's eyes are different colours, with his right eye a whitish hue. However, in the close-up of him after he first comes under suspicion, both of his eyes are brown. (00:12:02)
Continuity mistake: When Cody comes out of the turbolift with Slick, he's carrying a plain white helmet instead of his regular customized one. (00:00:49)
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)
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 Ahsoka is boarding the rescue gunship, her normally green lightsaber has a blue blade. (00:18:00)
Continuity mistake: When the Chancellor is being briefed on The Zillo Beast, Rex's kama is missing. (00:14:12)
Continuity mistake: When Dooku Force-throws some cutlery and dishes at Anakin, he gets a fork and a knife stuck in his prosthetic arm, but when he pulls them out, there is no damage to the protective glove he wears over it.
Continuity mistake: When Wrecker pulls Rex off Crosshair after the former attacks the latter for making insensitive remarks about Echo's presumed death, Rex's kama (kilt) is missing in the close-up shot. (00:14:10)
On the Wings of Keeradaks - S7-E3
Continuity mistake: When several of the clones are climbing up the ventilation shaft, Rex's kama (kilt) is missing. (00:04:17)
Continuity mistake: When Jesse and Crosshair are glaring at each other onboard the gunship, Kix has his right arm raised to grab hold of one of the handholds. When Jesse starts forward after Crosshair calls him a "reg", Kix's arm is suddenly down, but when Cody tells everyone to cut the chatter, Kix's arm is raised again. (00:07:00)
Other mistake: When Anakin is fighting some commando droids he suddenly has two lightsabers, one that he is actively using and another on his belt. (00:06:11)
Continuity mistake: When Hunter, Wrecker and Jesse are holding off droids at the cyber centre's front entrance just before they're forced to retreat inside the facility, Jesse's kama (kilt) is missing when he briefly emerges from behind a stack of crates to fire at the droids. (00:21:12)
Continuity mistake: The old photo Rex has of himself, Cody, Fives and Echo shows Cody and Rex wearing Phase II clone armour. This is even though the picture must have been taken before the events of season 3's Citadel arc that included Echo's presumed death, and Phase II armour wasn't introduced onto the show until season 4.
Continuity mistake: After Rako Hardeen orders a drink at a cantina, when the bartender pulls a bottle out from under the bar, it's corked when he takes it out and raises it to pour, but the cork is suddenly missing when he's pouring, although he didn't stop to take the cork out. (00:04:00)
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.