this is just something that DID people automatically know about...

heres what I mean...

think about something that you grew up with.. maybe its a favorite food..

now think about that for a minute..

you grew up with it so you know what that food looks like,what it tastes like and how you want that food cooked, or not cooked...

thats what having alters is like. people with DID start out with all the symptoms and problems related to DID including alters from before the age of 5.

because they have grown up with alters, even without knowing the correct psychiatric terminology for their symptoms and for their system of alters, people with DID automatically know how it is to have their alters and all the symptoms and problems associated with having DID.

So to answer your question alters know whether they are the only one or not simply because they have spent their whole life this way.