The 1987 is mentioned. So, it can be assumed that the 13 reported cases happened in the 1986-1987 timeframe.
More specifically, the movie begins with an interview sequence in which the date March 18, 1987 is given. Also, the incidents towards the beginning of the movie take place somewhere in the months of January as is mentioned by one of the characters in passing. As such, it can be assumed that the movie takes place in the late 80s, more specifically, in the early three months of 1987.
