Movies generally have a much longer production time than a year. So the script was most certainly finished before ST III was released in cinemas. So BTTF writers would only have knowledge of ST III if they also wrote it, and even then it’s highly unlikely that at the time of writing BTTF it would’ve been public knowledge (or even a made decision) Lloyd would be in ST. Getting most certainly wouldn’t have even started for BTTF.
I wonder if the time-travel plot of Star Trek IV was subconsciously planted.
Star Trek III was released in 1984, Back to the Future was released in 1985, Star Trek IV was released in 1986.
Did the writers watch Back to the Future, remember that Lloyd was in Star Trek III, and unknowingly self-suggest they write a time travel story?
Movies generally have a much longer production time than a year. So the script was most certainly finished before ST III was released in cinemas. So BTTF writers would only have knowledge of ST III if they also wrote it, and even then it’s highly unlikely that at the time of writing BTTF it would’ve been public knowledge (or even a made decision) Lloyd would be in ST. Getting most certainly wouldn’t have even started for BTTF.