Other mistake: When in the Swan boat, Marie has her arm hanging out with her fingers dragging the water, making waves. She is lying down and back in the boat, with a wing obstructing her view. Yet somehow the reflections of the waves show her face, perpendicular to the boat. Not parallel like her face actually is to the boat, and also somehow reflecting her face despite both a swan wing being in the way, and her being down in the boat out of view of those waves.
Other mistake: At the beginning of one of the school years, there is a sign on the front of the school that says, "Welcome back Class of 1980". A few months later, in December of that same school year, John Lennon is murdered. Since that class is graduating the following spring, the sign should have read "Welcome back Class of 1981", not 1980.