Great question — answering as the UphillTech team:
It was deliberate The website birthmoviesdeath.com published a Stephen King Commemorative Issue which contains an interview with Andy Muschietti in which he says the following about setting the movie in 1989: Another thing too, lest I forget: our movie takes place in the '80s. Obviously, we had to change the time periods for a bunch of different reasons. Mostly now because the '80s are to today what the '50s were to the '80s, so it just makes sense to keep the time scales to 27 years. Just move them up from 2016 back to 1989. So I think the answer to your question is: kind of. I wouldn't say the release date was planned to match the 27 year cycle, rather the movie was set in 1989 to match...
Full answer by sanpaco: https://movies.stackexchange.com/a/80923 (CC BY-SA 3.0).
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