Matt Smith is the 12th Doctor, or at least the 12th regeneration.
David Tennant cheating death, blow a regeneration, making his Doctor both the 10th and 11th regeneration of the Doctor.
I am well aware this view is not shared by fandom at large, but its my view.
Your view is nothing more than meaningless semantics. Whether or not the Doctor has used up 11 or 12 regenerations, Matt Smith is the 11th Doctor.