REALLY interesting mini rabbit hole you sent me down. My years selling tires taught me that the M+S designation was more or less dictated by the tire manufacturer and not independently tested, but it seems like M+S and "All Season" are terms that simply get conflagrated often. M+S seems to have a legitimate physical requirement, though it doesn't really have anything to do with the tire's capabilities. I wonder if the RMA actually certifies every tire available for sale, especially the flash-in-the-pan bulk buy tires from overseas that show up, sell out, then disappear from the planet (Chinese-based companies often register a brand name, make a run of low end tires without a real care as to quality, then abandon the name and design after the production run is over... I've never been sure if this is a liability shield, because the molds are cheaply made and wear out quickly, both, or something else). I suppose I was more talking about "all season" marketing, which legitimately doesn't have a definable meaning and doesn't necessarily appear on the tire. I have actually seen overseas websites for Giti and Ohtsu tires with "Summer Only" designated in the marketing materials, while the same tire model is sold here with "All Season" in the marketing material. It's a scientifically meaningless term. But I'm really happy to have some clarification that M+S actually has a technical definition from the RMA, unhelpful as it is at determining actual foul weather traction.