Not sure what you mean by the not covering the whole floor comment. My rear floor mat covers pretty much the entire rear floor. Unless you are talking about the lesser GM version?
Glad I clicked on this topic. My 2016 Denali came with a set of carpeted floor mats as well as the floor liners. However, the dealer didn't trim them and I never paid much attention till I saw this thread.
Will be trimming them tonight.