I think you have a good handle on the distinction between the technical (Dramatic dictionary) definitions.
However, I think there's a lot of overlap and the lines blur a bit when you're writing a story and the distinction is more easily felt than logically understood. In that sense I think Possibility and especially Potentiality are terms where the English words are much better at conveying their meaning.
e.g. in a story you can have examples of Possibility that seem to apply to things in the future, like this example from The Princess Bride analysis:
Once the cure is ready, everyone knows that it probably won’t work, so they resort to hoping for a (possible) miracle:
VALERIE (to Max): Think it’ll work?
MIRACLE MAX: It would take a miracle. Bye!
So maybe your term of evolution is good because the idea here is that the cure's chance of working is already fixed, and that's what they're discussing. But "it would take a miracle" could easily fit Potentiality as well; that's why you can't determine a storyform from just one scene. (although one clue here is that Probability fits as Symptom a lot better than Certainty)