sounds like you are looking for the hard and fast line to distinguish between ego states and alters. kind of trying to construct a list. to the best of my knowledge there really isn't a crucial feature that ego states have that alters lack or that alters have that ego states lack.

the situation is more like this:

ego states have features A, B, C, D, and alters have features E, F, G, H.

the upshot of that is that some people will have something with features A, B, E, F. is it an alter or an ego state? there simply is no fact of the matter.

there is a CONTINUUM between ego states and alters. it is a little like asking 'do i have high blood pressure'? if you make a graph by plotting the blood pressure of various people you will find that blood pressure lies on a continuum. there are a range of different blood pressures. then what we do is we create an arbitrary threshold which involves drawing the line somewhere or other. sometimes there are statistical reasons for doing so (to do with how much of an increase in risk of stroke or whatever). sometimes... there are pragmatic reasons for doing so (we wouldn't want EVERYONE to have dissociative identity disorder now - would we?).

so... there is no easy answer to your question. and what i think (this is my personal belief)... is... why does it matter? to appreciate that there is a continuum between ego states and alters and that there are many indeterminate cases kind of makes it irrelevant whether people dx you one way or the other (IMHO). in fact... to give you a dx kind of misrepresents the situation since it provides the appearance of facts when the actual situation is that... there is an indeterminacy.