There have been a lot of threads about this over the years, including a few I remember during the years when I was absent from posting here, so I've got no place to point to say "i heard it there." Even so, I'm pretty damn sure that most if not all of the original elements from the run of the series were kept in a belowground vault, much like the music that turned up during the 80s.
The reason I remember it was because I was astonished to hear it, especially given that Paramount wouldn't pay to store Apogee and EEG elements from TMP, so at least the EEG stuff got tossed during the early 80s.
Why keep stuff from the Desilu era but not stuff that had potentially greater recyclability?
if anybody can shed additional light either way, it'd be useful. If I'm wrong that the original elements are gone for TOS, then my argument for recomping goes with it, but that was honestly based on stuff I'd read here in years preceding this whole remastered/remesssed-with business. And as I recall, I wasn't even in favor of recomping at the time, though considering the alternative we wound up with now, in retrospect I should have carried signs and placards across the land for recomping.