Continuity mistake: When Cad Bane is taken into custody by a clone trooper, the trooper changes from a shock trooper to a standard trooper between shots. (00:14:40)
The General - S4-E8
Continuity mistake: When the 501st are pushing towards the Umbaran Airbase, most of the injured clones Kix drags away are missing their 501st markings, then in the next shot, they have the markings. (00:01:28)
Revealing mistake: When Grievous falls to the ground as the Gungans throw plasma balls at him, the lance General Tarpals stuck through his torso blatantly clips through the ground. (00:15:03)
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).
Revealing mistake: When one of the Mandalorians snags Ahsoka's right wrist with a cable, it clips straight through her head and neck in the process. (00:15:46)
Continuity mistake: When Anakin and Ahsoka are pinned down behind cover by the sniper droids, the damage the droids' blaster shots on the walls the Jedi are hiding behind changes whenever it's shown. (00:14:26)
Continuity mistake: When Krell is getting in Fives' face about who is going to take the blame for Fives and Jesse disobeying orders, the markings on Jesse's armour are missing. (00:21:21)
Character mistake: When Jesse says that he's "really not liking this", Fives calls him Hardcase when he responds with "don't get an itchy trigger finger." (00:15:35)
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)
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.
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: 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)
Continuity mistake: When Queen Miraj gets angry with Atai and Count Dooku, she throws her glass to the floor and the sound of shattering is heard. But after Anakin arrives, the glass is lying on the floor unbroken. (00:09:10)
Slaves of the Republic - S4-E12
Continuity mistake: When Ahsoka threatens Queen Miraj, she's holding her primary lightsaber. When she's shocked unconscious and falls to the ground, it's her smaller shoto that rolls onto the floor. (00:14:44)
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)
Continuity mistake: When Krell jumps out of the tower window, his blue lightsaber is in his right hand, but when he lands, his sabers have swapped hands, with the green one in his right instead. (00:12:21)
Character mistake: When Queen Neeyutnee thanks Jar Jar at the end, she erroneously refers to him as "Senator" Binks (he's a representative). (00:21:46)
Continuity mistake: Tup attracts Krell's attention by firing two shots at him, but Krell is then seen deflecting three blaster bolts. (00:15:41)
Continuity mistake: When Rex releases Fives and Jesse from the brig, Fives' kama is missing as he stands up. (00:11:00)
Continuity mistake: When Rex begins to question Krell in the brig, Fives' kama is missing. (00:16:55)
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.