Factual error: In the scene where Javert commits suicide, you can see the back side of Notre Dame in the background. However the river Seine does not flow in the direction as shown in the following scenes. The river Seine flows from the east to the west in Paris, not the other way round.
Factual error: When Sherrie and Drew are in Tower Records, the background song is I Remember You by Skid Row. But that album wasn't released until 1989, and the movie is set in 1987.
Suggested correction: The movie also says that Drew wrote "Don't Stop Believin" when the song came out in 1981. They also sing Heaven and More than words which didn't come out until 1989 and 1990 respectively. It's a musical that's full of 80's music, so they pulled all sorts of 80's music. It's not a mistake to have songs show up in a year, in a completely made up timeline.
Factual error: In the scene where Dave is playing cards with soldiers, some of the paper money being gambled is a design of U.S. money not introduced until about 30 years later.