Senate Spy - S2-E4
Continuity mistake: When Padmé accesses the holo-table with the droid factory plans, she puts her clutch purse on the edge of the table. After she guesses the correct password, the purse is absent from a shot facing her as the hologram activates, but present in the next shot. (00:15:56)
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.