Technically, there are 13 gods in the 12 as Nald'thal are actually two twin entities combined into one. It would track that the Twelve were the Convocation if it weren't for the wrinkle that Azem is among them when logically they would be the one who was missing. I personally think it's more likely that The Twelve are either Venat's group with Azem squeezed in there despite not being a proponent of Hydaelyn or the trace memories of Azem and the friend group that want around to save people of the world.