Yeah, LP outer covers were sealed in plastic shrink wrap in the U.S. at the time, but not necessarily in the UK and the rest of the world. As I said, Columbia Records at that time was also sealing the LP itself inside an inner sleeve that was a plastic bag. I remember sliding my mom's Johnny Cash album back into that plastic bag of an inner sleeve, and having a hell of a time getting the sleeve to stay in place on the LP as I slid both back into the outer cover.
When I joined the Columbia Record Club in 1962 or 3, my first month's selection (Johnny Horton's Greatest Hits) had a standard paper inner sleeve. So I guess by then Columbia had stopped using the plastic inner sleeve.