They knew which configuration would be sent for the tests because IIHS required it be the most "commonly sold" config, so they picked a specific supercrew model that made up about 70% of their sales to bump up the safety on.
Obviously it would be better if they had a deep commitment to safety and made every variation of every model maximally safe. But I'll take it. No such thing as absolute safety, so moves in a better direction are good.