Now that you said that, and I looked at Dunlop site and your correct the 3D is new and the 3M is showing as older. So maybe they did such a good marketing program on the 3D they sold out.
Not sure why they would tell me it was discontinued, unless they thought they could sell me 4 new tires.
I can tell those tires handle very well, I was impressed how well the car handles in both the snow and dry weather. I also impress the road noise did not get worse, you would expect the road noise to get worse with a more aggressive tread.