Does anybody know when the current style tab came into use?

Nasa Tom told us the pulltab was invented in 1962.

Does anybody know when the current stay on the can (yeah right, we dirt fishers know better!) tab replaced the pull off tab?

I remember vaguely when it happened, but it didn't really register. Seemed like it was a pretty fast changeover. Sometime in the 80's I think.

According to this link, the new tab came into existence in 1975. Check out the link. (http://www.squidoo.com/canpulltab)

What I want to know is why do people pull them off the can?? I never did even when I knew nothing about detecting... I pick them up every time I see one, even in parking lots. I guess it is the same mentality that throws cigarette butts out the car window or empties the ashtray at the bottom of the freeway ramp... but I really don't understand why folks pull the tab off the can. I wish they would go back the the early Coors push tabs. They had a larger and smaller pushtab, one to drink from and one for air.

Julien