I think ftp is asking an aerodynamics question, and BelArgUSA is looking at the aircraft operation side....
We all use abbreviatons and acronyms that are only valid in our own narrow field.
As an Dutch aeronautical engineering student, I was taught one set of abbreviations/symbols/notations for stability derivatives, angular rates, etc. etc., probably mostly of European/German origin. The moment I started reading American tech literature such as NACA/NASA Tech Notes, I had to get accustomed to a whole new set of notations. Then I went to work in France, and lo and behold, they had their own set of notations, with very little similarity to the ones I knew.... We live and learn.
So.... I think ftp would have been justified in asking what was meant with Mdi during his interview.
Maybe it was just "drag increase" Mach number? I.e., the same as Mdr or Mdd?
Oh, and... BelArgUSA...it would be interesting to know for an ancient like me exactly how Mmo, and the typical cruise Mach number, are related to Mcrit and M(drag rise). In the particular AFM on my shelf, Mmo is 2.04....
CJ