Both The BMI Repertoire and Allmusic.com say HEY NELLIE NELLIE was written by David Fromer, Jonathan Fromer, and Elbert Robinson. Gram Parsons recorded it on "Another Side of This Life: The Lost Recordings of Gram Parsons, 1965-1966."

HEY NELLY NELLY, on the other hand (note the spelling difference) was written by Jim Friedman and Shel Silverstein. It was recorded by The Back Porch Majority, Judy Collins, and Shawn Phillips. BMI says HEY WILLIE WILLIE is an alternate title.

I've listened to sound samples, and they sure sound like the same song.

I don't claim to know how these things happen; I only report what I find.

NELLY NELLY (according to BMI) was written by Gordon Menzies and Robin Watson. I have no idea what that sounds like.