Plus... this is Doctor Who. As former script editor Terrance Dicks put it, if continuity interferes with a good story, you ignore continuity!

There's a few rumours revolcing Matt Smith's pending exit now, that I find a bit intriguing.

It enlists the Doctor's lives in this order
1. Bill Hartnell
2. Pat Throughton
3. Jon Pertwee
4. Tom Baker
5. Peter Davison
6. Colin Baker
7. Sylvester McCoy
8. Paul McGann
9. John Hurt
10. Chris Eccleston
11. David Tennant
12. David Tennant
13. Matt Smith

So why is this intriguing, and why is Tennant listed twice?

Well, think about it. They've gone ahead and made Hurt's War Doctor count. Sure, he apparently isn't "The Doctor", but the "War Doctor", but this incarnation should still count as one life. Or regeneration. But then there's Tennant x2. This isn't the Meta-crisis Doctor, but rather the regeneration from "The Stolen Earth" that was induced by a Dalek. Tennant regenerated, but used his own DNA to make it seem like a healing effect instead.

Thus making Smith the 13th and final Doctor, unless he's somehow given some extra lives.

Now, if Tennant and Hurt don't count, then neither should Pertwee, as his Doctor is enforced onto Throughton by the time lords.

I'd continue the discussion, but Extended Edition goes live in 2 hours, and I don't want to spoil ALL the fun

Clearly, the regeneration issue is going to be the central conceit of the Christmas special.