I'd maybe make a hypothesis that a large portion of the space is "bad" smelling stuff: smoke or garbage. When people had covid-induced parosmia, it almost always seemed to be bad smelling stuff.
Intriguingly some of the really unpleasant smells never get through to me - I could probably work at a sewage works now. Worryingly I have next to no ability to smell burning, though I do now get the smell of natural gas (or the additive used to make it smell).
In addition to this, I sometimes smell scents that do not exist.
It makes sense for unclassified to smell worse than good, and it'd probably be the biggest category by a long stretch.
(Pure speculation.)