David Bird wrote:
Ah! But the numbers, as you say, aren't used within the show, so why were they used this time?
A narrator on a trailer is not a character in a story within the continuity of the show.
Matt Smith's Doctor is the twelfth incarnation of the character known as the Doctor. Matt Smith, the actor in real life, can also be referred to as The Eleventh Doctor as his version is the eleventh version of the character. Unfortunately, that's the reality, and the choice at this point for Dr. Who fans is to either accept it, or not. There's nothing we're going to do to change it.