We had 10% in our guidelines in 1984. When we implemented the fair dealing guidelines at the University of Guelph in 1984, 10% was the amount. It was, I believe, based on U.S. law on fair use in the U.S., which actually specifically allows for multiple copies to be made for teaching purposes. So, our fair dealing guidelines back then were based on what we believed to be fair practice in the sector at that time. They were not invented by Access Copyright. They existed before then.
On May 9th, 2018. See this statement in context.