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There's a difference between pre-islamic and pre-revolutionary. As a rule of thumb, pre-islamic art is uncensored, pre-revolutionary (but islamic) is censored, often heavily.
(I noticed part of your question I didn't see before, perhaps because you updated it.) During the early years of the revolution, there was a lot of religious zeal that saw some irreversible changes on a lot of fronts. Based on my general knowledge of Iran (I was born there, left when I was young, still have quite a bit of family there), I'd say that some art disappeared (but more likely into someone's cabinet than on top of the rubbish bin), but that quite a bit of it is tucked away for better times. Though, the longer those better times take to occur, the less likely these pieces will ever see the light of day.