I strongly suspect studio music "from the era," as felser suggested above.
I originally hoped for live recordings from Middle Earth, but consider that highly unlikely.
With 21, 20 and 23 tracks on CDs 1-3 respectively I'm starting to have doubts that the cuts are complete tracks (which would seriously piss me off, having preordered 😟). The recording of Amalgam's "Prayer for Peace" is 7:33, for instance.