Hm, I don't think you can base a story on characters.
Ah! You're quite right. The Screen Actors' Guild does draw a clear distinction, as defined on this page
. The way SAG's credit system works, story is one thing and characters are another. This way, the creative processes are separated.
That's really good to know, thank you. This will definitely improve my legal-ese.
SF "Based on an Original Human Created by SF2" 3
This reminds me of the quagmire created when the soap opera One Life to Live was canceled. ABC didn't want to lose 3 of the actors, so they were hired to portray their OLTL characters on General Hospital (soap crossovers were quite common on ABC shows), and a couple of other OLTL actors made guest appearances on GH (as their OLTL characters) as well.
After a year or so, One Life to Live was reborn as an online soap, and the legalese started flying. The actors still had contracts to appear on General Hospital, but ABC no longer owned their characters. This resulted in their OLTL characters being suddenly yanked from the storylines and those characters have never been referred to by name, ever again. It's as though that whole year (and certain storylines) never happened.
But now those actors are still on GH, playing other characters.