2003 CW Anakin vs Ventress is now canon again (Spoiler ahead)
So first of all, minor spoiler from the newly released novel Star Wars: Brotherhood, so keep reading with caution.
In this new novel, set after Geonosis but before TCW, Anakin comments on defeating one of Dooku's agents on Yavin IV, but he didn't recognize it was Ventress due to the rain. The author of the book himself confirms Anakin is mentioning that duel, wheile telling us why he wouldn't later remember Ventress in TCW: "The idea is that when he fought Ventress on Yavin IV in the Genndy series; it’s raining, it’s fast, and then it's over. He’s just like, Dooku sent someone after him. He has no idea who it is."