I have scoured the internet trying to find the year that the late Bobby Sands wrote "Back Home In Derry" and cannot. At first I thought he may have written it during his second and last stay in prison but I cannot find anything to support that. There has to be a date out there somewhere I suppose but I cannot find it (I spent about an hour one night searching).
I also can't find any evidence that Lightfoot lifted anything, not even a particular style from any Irish folk music. Nothing in regards to this is dated except for Lightfoot's "The Wreck". That being the case, it appears that others' have attempted to use Lightfoot's song.
It is very common for musicians to follow a certain "style" for a particular song. If you think about it, everything that a musician writes has been influenced by something or somebody. They may like the sound of a chord progression in one song and tie it in with something else. Listening to other famous musicians talk about where ideas came from I have yet hear any of them say they are 100% original. Coming up with any new song all one has is to rely on what they have already heard. Probably mostly on a subconscience level too.
"The Wreck" is an orginal Lightfoot masterpiece and if there was any suspicion about where it came from, you can bet somebody would have sued him because of the HUGE success and shot in the arm that song was for Lightfoot. If it is a commonly used style in Irish folk music than so be it. That's what it's there for.