Purple Chick's Deluxe Edition of Let It Be is six discs of material almost entirely from January 1969. The first two discs are the released and mostly finished (but unreleased) tracks in stereo and mono. Discs three and four are compilations of mixes made by Glyn Johns throughout 1969 and into 1970 (aka. the Get Back Acetates), while the final two discs are session outtakes and alternate mixes.
Many of the take numbers on this set are "DDSI numbers", from Doug Sulpy and Ray Schweighardt's "Drugs, Divorce And A Slipping Image", a book that I don't own that was first published in 1988 chronicling the recording sessions of January 1969. It used numbers in the form XX.YY to refer to the takes; XX being the day it was recorded and YY the song or take number from that day. So 27.63 is the 63rd song recorded on January 27 1969. The book was revised (including some of the DDSI numbers) and published as "Get Back
- The Beatles' Let It Be Disaster" in 1997, and a revised list of numbers was published in Doug Sulpy's "The Complete Get Back Sessions" in 2001 -- this would appear to be the version referred to by Purple Chick in this set. (The book has been revised and re-released under its original title on November 15 2007, so looks like the numbers will change again...)