No the seat of Azem was always there, that is confirmed with the side stories.... at those were pre soundering.

They always were 14 - Venat retires and our old self takes the seat for some time, dealing with emet and the others too, as said in the side story - the final days hit - "we" go ??? and dont side with either side and leave, letting our seat empty - they summon Zodiark - Venat gathers followers (maybe already before that) and at a later point she becomes hydaelyn and splits the world.