Many recordings have long ago been digitised using the standards of the day and the masters lost or destroyed, or were simply recorded digitally at CD quality in the first place, and that's all there is. So while it may seem perverse to be going back to pre-CD recordings as a source for high-resolution releases, in many cases - at least where the analogue master tapes still exist - that's the remastering engineer's best bet at coming up with something 'beyond CD'.
We've seen that a lot of late in the rock music field ... and the results can be spectacular. That's certainly the case with one of the most recent reissues to come my way, Gimell's 40th-anniversary high-resolution release of one of its first recordings, The Tallis Scholars' 1980 reading of Allegri's Miserere in the Chapel of Merton College, Oxford. In the 192kHz/24-bit release, the recording sounds spectacularly fresh, showing just what today's hi-resolution formats can do with fine sound from the past.