What that means is that the C0EX (EXECUTIVE) fare is identical to the Y3FR or YFR (FREEDOM) fare on some city pairs. You don't need to use U/G cert because you'll be purchasing an Executive fare. (If you're a customer and see that the Freedom fare = Executive fare, what would you get?)
As far as I know, there are no M fares on the US now under the new fare structure.