The version I posted (unattributed) is from a German site that has more pop-ups than a horse has hairs. They didn't attribute it there, either, other than to say it's the version (lyrics) used by TMTCH. So, that said, I'd think that the attribution as to authors that you found (and also backed up by Tracy Grammer's site) is probably correct. Looks like a co-written piece in which they share credit for both lyrics and music.