Not sure about the NEK, but formaldehyde (PFA) appears to have been banned in the US in 1982, Canada in 1992. But just like the Olympics, there will always be 'dopers'.
http://www.intentionallydomestic.com/friday-food-fight-is-there-formaldehyde-in-maple-syrup/
http://www.theglobeandmail.com/news/national/sticky-fingers-beating-the-bush-in-search-of-maple-syrup-cheats/article17261481/
Perhaps in the 70s, just as it is now, it's just closer and more convenient to get to Quebec from the NEK than just about anywhere else in the World.