It was in the late 90s; I started teaching in the 99-00 school year, and did purpose-written pieces that spring, and I was told that UIL had been doing this for "a couple of years" by then. They did this because there were a lot of directors who would find out what piece their group would read...buy it...and then practice it in rehearsal. When they got to UIL, they weren't sightreading the sightreading piece.