OK I got to the bottom of things just a bit.
 
The "Lamacq Sessions 2001" are in fact the "Evening Sessions" on the BBC compilation release.  My version here contains 1 extra track that I believe has no title.
The "Plataeu Sessions" seems like it's going to be "Unreleased Plateau Remixes" though I haven't vetted all of the tracks yet to be sure.
 
That just leaves me with this "30 min improv session" to figure out.  The only track I quickly recognized last night was a version of Toxygene.
I'll report back when I know more.
Thanks much!