My guess would be that Howe has versions of these tracks with him playing on them (and perhaps no Haun). That is, these aren't backing tracks of the versions on Union: these are unused backing tracks.
This release includes the entire recorded output of the Howe/Haslam collaboration: one impossible-to-find single and one track from a Yes tribute album.
Look to be all from the post-GTR sessions. Phil Spalding was talking about these getting a release last year, so this would appear to be where.
Henry
Bookmarks