Actually it did happen. I just inherited the "Headgear Hell" blog so you can go there and read the long version if you want, but we lived an hour north of Seattle, my brother was an orthodontic patient at the University of Washington Dental School. He wore his for 9 months "tied in". There is an article in the American Journal of Orthodontics from 1971 by Armstrong "Controlling the magniyude, direction and duration of extraoral force."
The longtime editor of the "journal of clinical orthodontics" wrote an editorial around the same time urging all orthodontist to agree to require full time wear for all headgear patients. The original author of "Headgear Hell" had an ortho that gave a speech in front of an Orthodontic Association meeting entitled "24 hour headgear: I like it.". So I think his story is true.
My orthodontist who was not part of the UW program absolutely would have "tied" mine in if my mother had her way. As it was I was told to either wear it all the time or it would be tied in. Which, of course was almost the same as having it wired on, the difference beine able to eat and drink and brush easier.
I will turn 60 in two months. The sixties were a long time ago and so much has changed, but it did happen.