Hello,
I cannot found completed quests on tbc vresion ( http://wow.gamepedia.com/API_QueryQuestsCompleted don't exist).
It is for this reason than quest bot don't works correctly.
The only way to bypass this probleme is to record in WRobot when quest is completed in game, but it is not reliable (and only quest completed when WRobot is not running will be in the list)