Late 70s. Our house was built in 1979 and took bentonite into consideration when it was constructed. Slabs were designed to ride up and down. Penetrations in the basement slab could handle it and when I built walls down there I was instructed to hang them from the ceiling with provisions at the floor for the slab to move independently. We had no problems.
BTW, bentonite is not limited to the Denver area. We had to deal with it in California when my employer at the time put in a lab north of Hollister in 1989. We dug down about 3 feet and put in engineered fill before pouring the slab for a 40 by 140 foot ground plane for an EMC lab. Then paved out a few feet around the perimeter to keep water out of the fill. That was an expensive way to build a ground plane. Haven't done it that way since.