I was at the dealership on yesterday and decided to take another look and every 2019 XTS and CT6 had this imperfection.
Sorry, but I just thought I would share so if anyone does notice it they will know that it is probably not ding from a car door.I have checked my 2019 (CT6 #3) and I haven't noticed the imperfection as described. Now I wish I hadn't looked, because I discovered a loose gap between the entire plastic lower trim panel and the upper rear fender. These vehicles are hung together with plastic clips. It's a large body panel wraps from the wheel wells all the way around the rear bumper. I was hoping that I would get a CT6 that stays intact within its first 3,500 miles, but at least this is a minor flaw that can be repaired at its next service visit, I hope.