No, but Sister Mary Bernadette of the CMRI was for almost 2 decades. She was a traditionalist as early as 1967 and by 1970 she and others believed that Paul VI was not a true pope. So, although "sedevacantism" may not have been coined, it was definitely in the Traditional Movement as early as the late 60's.
Yes, I know it was around, few and far between tho they were, mostly they were the original home aloners but they never coined the term. Not sure who coined it, but by the early 80s someone did. I knew some home aloners, sad situation that.
But that youtube shows a sermon given by a trad priest of about 30 years in about 1985, who prior to The Nine basically never heard of it or had any reason to consider it, decided that he needed to explain to his congregation something that they most likely either never heard of but would, or only knew so little about that they couldn't even pronounce it. The reason he even talked about it was as he explained - because the novel idea was spreading among priests and laypeople.
This is why he was explaining it - because except for a minuscule fraction of trads, nobody else ever heard of it. Nobody ever heard of it because it was something new, a new idea that was added into the crisis. The reason it was a novel idea because it is found nowhere in tradition. And although it was around, essentially sedeism did not exist prior to The Nine.