He actually did Jugband Blues on Saucerful of Secrets, and others such as Apples and Oranges, and see Emily Play but they never made it on any Floyd albums.
You are right, I just looked at the discography and he's listed as guitar and vocals on Saucerful.
http://www.pinkfloyd-co.com/disco/saucer/saucer_album.html
But just has one tune. Looking at the rest of the discs, it's clear he dropped out after Saucerful. He shows up on Relics but that's just old stuff released after the band was a success.