True. They really should've spelled it out more in IM2, no matter how briefly during the actual film. I feel the special features piece to fully identify him as such was their way of trying to acknowledge that they didn't do it in the film, editing, rewrite or what have you and it got lost along the way.
Still, Feige acknowledges Shane approached him to change Mandarin and he approved. I'm curious to know how he was written in the film prior to Shane Black's approach to go with what we got.