I know the literature seems to suggest PCS prognosis is excellent. Yet everything on pituitary seems to suggest damage doesn't get any better.

Is there any way to distinguish one from the other?

I saw a blog from a former hockey player (which was pulled), but basically suggested PCS of more than 30 days was likely due to pituitary issues:

If I learned anything from it that I can pass on: the pituitary gland plays a huge part in Post-Concussion Syndrome, and our writer contests that it should be checked in all cases where PCS extends beyond 30 days.
-Jason Bourne