I may not have all the details right, but a guy works for Fripp and company cataloging tapes and snippets, etc from everything Fripp related. He used to post interesting ones on the DGM website and they are getting released on CD every few months.

The best stuff has mostly been plundered for Tour Boxes, but since I just got Number 5 in the mail, I thought I might look back and see what the gems were from the sets.

Volume One
-The Greg Lake vocals on Cadence and Cascade
-Some rough instrumental stuff from Exposure--Disengage and North Star
-The early version of Larks III that includes a the verse riff from Sleepless

Volume Two
-An actually listenable rough cut of the Devil's Triangle
-A minute long instrumental version of Mary from Exposure that is very, very pretty.
-Two minutes of unused strings from the title track to Islands
-A version of Fashionable from the Vrooom Sessions that shows a lighter, nimbler version of what the Double Trio could have been. (Though I like the bone crushing thing they became).
-10 minutes of Fripp, Wetton, and Collins jams from the Exposure sessions. Imagine Asbury Park except in '78 and you wouldn't be too far off.
-Fripp and Gunn doing three minutes of Fracture at a soundcheck (is this from Fripp/Sylvian? Or Sunday All Over the World) is interesting, but not earth shattering.
-About 5 minutes of Fripp, Bruford, and Jeff Berlin from a jam session around 1980.

Volume Three
-Fripp, Bruford, and Berlin actually playing parts of Discipline!
-There is a little bit more of Fripp/Wetton/Collins
-There is like 20 minutes of fly-on-a-wall stuff from the Double Trio for people who are into that.

Volume Four
-The unspeakably gorgeous instrumental trio version of I Talk to the Wind that has ended up on a tour box
-12 more minutes of Fripp/Wetton/Collins
-"Buzzsaw" which is about 8 minutes of the Double Duo embarking on something halfway between the Projekcts and what they became.
-The isolated guitar from Lady of the Dancing Water, which has some seriously beautiful chords

Volume Five
-Some isolated soprano sax by Mel Collins from the Starless recording.
-A minute of nice interplay from the sessions for the Waiting Man. I could listen to a two hour loop of this stuff.
-Fripp working on the solo for Matte Kudasai. Three minutes of that Fripp sustain.
-A fantastic early run instrumental through of Ladies of the Road with just bass, drums, and guitar. Fripp guitar sounds so grimy. This track has convinced me that he actually has rhythm.
-A completely different guitar solo for Prince Rupert's Lament. (I guess he recorded four)
-1'45'' of interplay from the end of Neal and Jack and Me with a guitar synth solo. This is something else I could listen to on loop.
-15 minutes of fly-on-a-wall stuff from the the Nashville sessions where they are working on an early version of Frakctured.
-A full run through of the title track of Islands with just guitar bass drums tron and vocals. The guitar was apparently a studio guide for Keith Tippet. The lyrics aren't done yet, but the gorgeous guitar makes this version well worth hearing. The arrangement is very similar to the one they used when they played this live in '71. This has definitely ended up on a tour box.
-Some of the horns, keys, and guitars from Happy Family, but no bass and drums. It sounds like people trying to annoy each other with their instruments.
-"Level 6", in which pieces that would someday be "Happy to Be What You Have to be Happy With" are in an instrumental arrangement similar to Level Five.
-Bass/drums isolation mix from Thela Hun Ginjeet

Five is the best one out of these ones that have had physical release so far. I don't know what to expect out of volumes 6, 7, and 8. (I think they were 8 volumes). It seems that the sets become more geared towards King Crimson as they go, and less heavy on the stuff from Exposure, soundscapes, Fripp reading poetry on BBC radio, etc.

These sets are by definition for the hardcore fan. The revelations don't come often, but there is some wonderful listening in here, mixed in with things that I will likely never listen to again. Frankly, the amazing liner track-by-track liner notes are what pushes them into the "worth owning" category for me.

I do know that one of the later volumes has the gorgeous trio version of Cadence and Cascade that sounds like it was made by Belle and Sebastian.