You are not immediately recognized as Azem. You are only recognized as a having a soul that is from a fractured Ancient soul because you have the echo. You are not recognized as Azem until you meet Hythlodaues. When Emet complains you don't remember, he wants a generic Ancient to remember the fun times in perfect Amaurot.
If he knew you were Azem, Emet would have needed a different plan.