Had the same question on a Townsedan I bought that was restored. Heard about the sound difference when knocking on it so took it to a glass replacement business. The manager knocked on it and said it was laminated. Heard about the double image idea so angled a business card and it showed double. Being the doubting type and concerned about safety, I went ahead and pulled the top of the frame. "Low and Behold", it was plate glass. Replaced it before ever driving it again........