I've often thought about that too.
He said he used the regeneration energy to heal but siphoned the rest to the hand. He didn't give the energy time to finish the regeneration.
You can take this to mean that he stopped it before he changed his appearance, and it still counts as a regeneration. Or you could say he stopped it halfway through so it doesn't count.
I credit the younger Smith Doctor as a product of his diminished regeneration energy.
And I'd still call Smith the 11th Doctor (not counting the potential Hurt Doctor). He'd still be the 11th incarnation (unique appearance and personality), regardless of what regeneration he is.
Yeah, either way the BBC isn't going to stop at 13 Doctors. We fans won't allow it. lol
I guess I'm just getting grumpy in my old age.