Well the general said all 13, so no really reference that it was the 'last' doctor.
Also I wonder in 'Lets Kill Hitler',when the Tardis said 'regeneration disabled', it was not because of the poisoning but because he could not regenerate anymore. But then there is the whole confusion on how much energy River gave the Doctor, then in the following season the Doctor using some energy to heal Rivers hand.
Continuity would be best served if Capaldi was the last and 13th Doctor, he regenerated 'old' because he used the last of his regeneration energy. Series 8 would deal with the Doctor now being 'mortal' and the search for Gallifrey. He finds Gallifrey and then gets a set of lives from the Timelords.