AIR NEW ZEALAND WAS THE FIRST AIRLINE TO USE DE RATED TAKE OFF IN THE Dc8-52 BACK IN 1967
Now, I don't know for sure who started things off, but Wal Stack (boss QF performance man), in the late 60's/70s used to do some time as an Industry Lecturer in AeroEng at Sydney University.
His stories relating to reduced, specifically, and probably derated (too long ago to recall and, in any case, I don't think I understood the difference as a young chap), takeoffs suggested that QF had been doing this sort of thing for quite some time.
(Not an Air Kiwi basher as I have worked for the good folk on occasion with fond memories.)