And this is exactly why Noah didn't have any room for the Ligers.
At the time the movie came out, there were still 10 cities unofficially in contention for the two new NL spots, the finalists were cut to 6 in 1990.
There was never a time that there were 4 finalists.
It was an educated guess, but they nailed it. Especially considering the team wasn't referred to as "Miami" until 2012.