The movie takes place in 1966 but all the Bruce Springsteen songs that were featured weren't recorded until the 1970's so they wouldn't be relevant. All the other songs on the soundtrack were actually recorded and released before or during that time frame so they fit and made sense.
The prom sign says congratulations class of 1969. The parents say they are happy they are sending Jill to a women's college. Sarah Lawrence went co-Ed in 1968 which would be at least a year before Jill attends.
When Sheik and Jill leave on their trip to the New Jersey shore, they cross a large bridge that has the slogan "Trenton Makes - The World Takes" on it. This bridge actually takes you from Trenton into Morrisville, Pennsylvania.