I think we all agree that, provided Oda doesn't give them further insight, they have very little material to work with. Why would they only use that chapter and not the cover story? For what reason? I say they'll use whatever they can get their hands on, probably make up some stuff on their own.
I'm just saying it's a possibility. And I doubt they're gonna make up stuff due to the high probability of them being covered in the manga unless the stories were made by Mr. Oda himself to use in the anime due to time constraints in the manga.