i think part of the difference is a difference in degree.

part of the difference in degree could come down to lack of amnesia for times the ego state is out. (amnesia is required for DID dx)

part of the difference in degree could come down to lack of their being in control. so... talking about them instead of switching into them i guess.

part of the difference in degree could come down to how elaborated they are. so... 'fragments' rather than 'identities'. e.g., one feeling state (e.g., panic) without elaboration into a name and memories and stuff like that.

part of the difference in degree could come down to what kind of personality they are. so... like how that article differentiated DID from less extreme conditions on the basis of whether there was a split in the ANP or not. so, on this definition it wouldn't matter how many EPs there were without a split in the ANP the person would be DDNOS or complex PTSD and not DID. though... i think they did say something about how it is DID if the amnesia requirement of the DSM is met. so... no hard and fast line methinks...