Just to be clear: "when" was the correct answer for the plastic bags question.
It was not until 1982 when I got a car.
It was not until 1982 *that* I got a car.
The first construction is a fragment. When I read it, I'm still left wanting a "that" (like, "It was not until 1982, when I got my car, that I graduated from high school.).
Also, evidence is singular, so the verb should have been singular.