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)
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.
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.