Michael,
I am attempting to understand what your concerns and questions are. You seem to be returning to the matter of realism versus a manufactured portrayal of a subject.
There is no argument from me that a person could be posed and made up in such a manner as to give a representation that had nothing at all to do with that particular persons real condition. Does that negate it's import as an image? I would have to say "no" it would not negate it at all if, in fact, it was that the photographer wanted to impart a message to the viewer and was able to do that with his portrayal of the subject. If that were the case, how would that be different then a photographer doing a table top study or a landscape that is favorably photographed? It would seem to me that the only difference would be the choice of subject and that a preceding intent existed, on the part of the photographer, to impart a message. Would that be a portrait? I would guess that most would feel that it was a portrait, since it was an image portraying a human being. It, however, would not be based in a realistic depiction of that particular person. It could still be effective, in my estimation, if it portrayed something about the human condition.
There is another aspect to this, as I see it. That is portraiture in which a photographer wishes to render the person which he is photographing that would be representative of that individual and it may or may not portray some aspect of mankind as a whole. Again, that would seem to me to be protraiture.
This has gotten quite far afield from your original question of snapshots in comparison to portraits. I don't mind discussing this if this is helpful. I just don't want to be quilty of diverting the subject from your original intent.
Regards,
Donald Miller