She Moved Through the Fair wasn't intended as a revenant song at all; John McCormick seems to have substituted "dead" for "dear" when he made a commercial recording of it; probably by accident. The rest is history (and a great deal of romantic misunderstanding).

I've read the Shields piece, which is convincing. Although versions of The Grey Cock occasionally show up with ghosts in them, these can invariably be shown to have been imported from other songs: usually Willie O or The Unquiet Grave, from what I remember.