Glen Holland owns a Chevy Corvair throughout the film. The car at the beginning of the film is a 1961 model 500 (the base model with bench seats), but at the end of the film it is a 1964 Monza (the top of the line model, with bucket seats).
All the American Sign Language used in the movie is accurate. When Iris tells Cole to open the window, Cole's response is not translated and she says "don't bust my butt." What he signed was, "Tell him to open the window himself."