Situation: ( not saying this is smart play but ... if ... this were to happen )
Titanodon has Ballad of Courage ( Slow and Fast cancel each other out ) and opponent plays Enfeeble on it, giving it slow again.
Ballad drops off, now Titanodon has double slow, which as far as I know has no additional effect besides simply being slow, correct ?
Then a new Ballad of Courage is played. Does this cancel both Slows ? I assume, yes.