I was wrong. Evidently the Super-8 format was introduced to the public in ‘65. I thought it was merely developed then.
I still think it’s highly unlikely more than a very small group of people were using it until the mid ‘70s.
In the mid ‘70s they came up with a cartridge format, that become quite popular for a while.
http://motion.kodak.com/motion/Products/Production/Spotlight_on_Super_8/Super_8mm_History/index.htm
Super 8 cameras really didn’t hit the scene until 1968 or so. I bought one of the first ones that came out. Just two weeks ago, I transfered a Super 8 film that I shot in 1971 to DVD.