Alters can definitely go unnoticed. It isn't like they jump out and say "Ta-da! Herrrrrre I am!" I told this to one therapist and she replied "Oh, so you don't have DID then. Because DID would be like that."
Ummm. Yes I do, and
No, it isn't.
Alters just slip and slide behind the eyes, doing what they gotta do without too much fanfare.