Oh, I thought he was just going for "prominent and uncredited."
What I was really going for was the impact on the listening experience, the "bolt from the blue" factor when the female backing vox kick in (especially, but not only, if they are doing a non-lyrical solo, a la the Floyd & Roxy tunes).
So I would rule out "Gold" just because Stevie doesn't sound that impactful to me. I'll have to listen to "M&S" again, since it's been a while. And I think I ovelrooked Oleta getting a titular credit on "WIC", so I'd draw the line with her on the other side of it.