[markreed]

I'm no expert but I imagine the material in question are in obselete or obscure computer formats, so there had to be (as alluded above) tech build or adapted to allow the files to be recovered, fed into new technology, and then mastered to meet the audio standard.

As an aside, Karl Bartos had to source JAZ and ZIP drives to recover his 1976-91 demos for last years "Off The Record" album which was made of songs he wrote for Kraftwerk that they did not choose to use. Same thing really, finding a way to recover material locked into old and largely unusable technology.