I thought both of you may be interested in learning that Glen had been playing the Jimmy Webb song, "Adios", for quite some time -- with Jimmy.
According to a blogger or linked blog on chimesfreedom:
“Adiós” is not new for Campbell....Webb has explained that he and Campbell used to play the song all the time in various places, including their homes, hotels, and dressing rooms.
This info supports at least part of your theory, Cowpoke, when you posted: "I imagine Glen continued to sing these songs (referring to the 4 songs on JW's Suspending Disbelief that Glen recorded for Adios) thinking "one day I will release these on an album".
Kim Campbell has also mentioned in several recent interviews, print and video, that all the songs on the album, 'Adios', had been on Glen's bucket list to record.
Glen must have been quite taken with Jimmy's "Disbelief" album.
From: http://www.chimesfreedom.com/tag/jimmy-webb/ (May 18, 2017)