http://www.film-tech.com/ubb/f1/t008255.html
Brian Dooda draw a very specific timeline when Mono and Stereo-tracks has been used and he backs it up with the noise-reduction types, which were used back in the days. In Conclusion Dr. Cooper nailed it with Dual-Mono and silver-wook with the compatibility of the sound system used in different theatres. 😃