I doubt that all tire brands made by Michelin used - or at least now use - the same compounds.
I read the sidewall materials description on the original Michelin LTX M&S tires that came on my Class C and it definitely read different than the sidewall description on the new type (at the time) Michelin LTX M&S2 tires that I put on our RV in mid-2011. The sidewalls have at least one of their plies made of some exotic-sounding new material. I'm hoping this at least partially helps to solve any premature sidewall cracking problem that Michelin may have had.
Unless the other tire lines that Michelin manufactures also had their names changed in what they are called, too - to account for this same new sidewall material - probably only the Michelin line is using this new sidewall material. Of course that could be due to the fact that only the Michelin line needed a sidewall materials improvement.
By the way, would someone refresh my memory on how nitrogen is supposed to help with tire dry rot .... or does nitrogen only help with maintaining tire pressures over the long haul because of the larger percentage of nitrogen molecules (which are larger than oxygen molecules) reducing the amount of pressure loss through the tire material.
