"The late 1990s" is never stated, Sparvid. The dialogue says "It is the end of the 20th Century" (paraphrased), which is non-specific to exact date. Period. The writers could have set the film in 1999, but they didn't. Let's still to the facts, please. Pin-pointing 1999 as the specific year, by reading into "the end of the 20th Century," is a big leap of faith. We can't ask the writers, because they are deceased. But, assuming the precise year is presumptuous. That's the point.
(By the way, the 20th Century ended on December 31, 2000. Centuries start at 01 and end in 00. The 20th Century was 1901-2000. So, the film could have been set in 2000.) People can post a thousand arguments, but it still won't move the facts and won't force the dialogue to say "1999," so resistance is futile.
"Remember, to avoid fainting, keep repeating: It's only a movie. It's only a movie. It's only a movie. It's only a movie. It's only a movie..." 
