Another thing that bothers me is the fact that when Marty and Jennifer goes to 2015 at the begining of the 2nd movie, they arrive in a future in which they are still there, 30 years older.
They should have gone to a future in which they mysteriously disapeared in 1985, the morning they were supposed to go to the lake, and were never seen again.
Think about it. It really doesn't make sense otherwise.
And by the way, Calvin Klein Marty is called Pierre Cardin in France...