Huge knowledge gap between “can be crystallized” and “behaves as a crystal”.
When enquiring about “physical state”, one has to be explicit about the conditions. Which is where STP comes in (standard temperature and pressure).
If you crystallize THCa, and have “isolate” at 99+% purity, then decarboxylate, you have THC isolate no?
You’ll also run into folks calling THCa isolate “thc isolate” as distinct from “isolate” which is often shorthand for CBD isolate.
Used to be you could get a PhD for crystallizing a single protein…”I tried and failed, therefore it is impossible” is certainly one way to approach the problem, but it wouldn’t fly in a crystallography lab.
Have you looked in the data dump?
Most everything you’re asking has been published 30 years or more ago.
Consider reading everything grandfather has written.