Interesting! One person admits that they took something from someone else, who in turn did the same: "...I learned about 10 years ago from a musician originally from Tennessee who said he had changed a tune enough that he gave it a new name-...", and complains when someone else does likewise? i.e. "...The A part is changed somewhat from what I know, although the chord pattern is intact..."

If identical chord patterns are to become the basis for "owning" a song, we're all in trouble.

If you've got something unique, get it published, or record it, or mail yourself a cassette tape of it in a sealed envelope, or get a copy of it notarized and then challenge the "offending" parties when the situation arises.