Regarding the Md. Even if the margin between Mmo and Md looks small, it’s actually quite large.
Once you are past Mmo, the transonic drag rise rapidly starts.
AFAIK, to get anywhere near Md, you would need a deliberate dive with engines running at high thrust for a lengthy period of time - otherwise the plane just won’t accelerate.
I cant find it now, but if you dig up the CS-25, there is a clearly described maneuver, which is used to establish/demonstrate Md. I don’t remember the details, but it’s waay out of normal ‘airline’ envelope. You just won’t get that far, unless you are in a major upset.
I hope that someone with more knowledge of aerodynamics and flight testing will pop in and elaborate on this.