These are alternative takes from the studio sessions. From Bandcamp
So, how I figure out is that Geir played a series of live controlled takes in the studio and then some were picked for the album, and these alternative versions are just alternative takes on the same tracks from the same studio sessions. I think this was a pretty common strategy back in the 90s before sequencing the whole track in a DAW became the norm? Like The KLF's Chill Out in which case the whole album was recorded multiple times live and then the best version was picked.
Anyway, for a person like me who has heard the original Substrata about a million times, this is a pretty interesting release. I like some of these versions better than the original release and some original versions better.