As Jack said, it's not flat! In the 1965 Beetle VW put a slight (hardly noticeable curve) in the windshield in order to prevent breakage. It also got bigger for better viewing. The breakage was mainly from passengers hitting the windshield even slightly with their hands. I know because I have replaced many of the broken windshields! If you need proof, put a straight edge on your '65 up windshield.
