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)
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)
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.