When the Feb. update came out, I never got the Mixed 5 track. The hotfix update didn't fix this problem. I have tried uninstalling and reinstalling the game to no effect. At the time of the update, the only mod I had installed was my own, which is an AI name mod. In the BagEdit thing I noticed that I had Mixed 5. (though I'm not sure whether or not this is the actual track because American 2 (II) is American 3 in BagEdit)
EDIT: I'm stupid and didn't notice the modify button. Haven't used this forum much. I don't have mixed 4 either.