[possible spoilers in the question]
This question Why didn't any Death Eaters come back as ghosts had a couple of answers that rely upon the same quote:
Having chosen a feeble simulacrum of mortal life, ghosts are limited in what they can experience. No physical pleasure remains to them, and their knowledge and outlook remains at the level it had attained during life, so that old resentments (for instance, at having an incompletely severed neck) continue to rankle after several centuries. Pottermore – Ghosts [emphasis added]
One could certainly envision ghosts who essentially repeat the same information ad nauseam. Frozen knowledge would, I should think imply that a ghost is unable to acquire new information.
Yet we know that in
Goblet of Fire
Harry procrastinated on examining his "egg". After a hint, he utilized the luxurious bath on the advice of Cedric Diggory. Even then it took input from Myrtle for Harry to solve the riddle.
Myrtle was able to assist Harry based upon her prior observations. Thus, Myrtle had to have acquired new knowledge.
How can knowledge be "fixed", yet the ghosts clearly demonstrate learning? In a different example, the ghosts also learn new students' names, or know about submitting requests (and the subsequent rejection) to join a headless hunt society.
I hope this question is not too opinion focused. It is the answers to the previous question that raised my curiosity.