I used to try to research every episode for other people's missing scenes just to make sure I didn't accidentally duplicate something, but that got old. I just don't bother anymore. Similitude is coming up, and it would probably take me a month to read every Similitude fic out there.
Besides, this is fanfic in the first place. We're all using characters that don't belong to us.

(Having said that, I do find it mildly irritating if an original character I created gets borrowed by someone else and is changed really significantly in the process -- like suddenly he turns into a she. But again, I don't own this universe. So ... whatever.)