Speed endurance the key to *all* 11/12second sprinters?

1: Yes
2: A limited amount since these were high school kids at the time and the HS meets served for a great deal of special prep based on a limited tolerance they would have had at the time.
3; The SPP would be the high school comp period and again after a short break the summer meets. For such athletes, it woud be a matter of proportion, as there would be speed and some SE done but it’s proportion relative to aerobic and general conditioning would be much smaller than later in a career.