"manufacturers need not receive premarket authorization for existing products that are the subject of a label change only (e.g., a product that has a new name but is otherwise identical to the predicate) (see also question 17). "
https://www.fda.gov/downloads/TobaccoProducts/Labeling/RulesRegulation-sGuidance/UCM436468.pdf
So, STG renaming Dunhills is not the problem. The problem is when did STG start remaking Dunhill and I think it was after 2007. Maybe it can be argued it is the same product that Murray made prior. And my guess is STG sourced different leaf, came up with different process, different casing, etc., so it is not the same as Murray's as many have pointed out here. Unless the FDA backs off before 2021, I think "Dunhill" is most likely finished as far as the U.S. goes.
I have plenty of Dunhill so it doesn't really matter to me. What does matter is I like to try new tobaccos, even if just a tin or two, and new tobaccos introduced to the market will most likely become a thing of the past here. So, my cellaring strategy going forward is to accumulate a wide variety of tobaccos I've never smoked before so that I will still have the "new tobacco to me" experience in the future.