It's not always easy to know if the magical theory etc was created by that person or is just absorbed into fanon or whatever is it?

I just read 'The Boy Who Lived Twice' and have an urge to write Unspeakable fic now, but the Unspeakable practice etc in that fic was all lettered's I think, even though it will forever be how it should be in my head, so I couldn't use that without asking first and I wouldn't.

It's very complicated.