Mission music question.

I've been wondering about this since beta. There are several mission music files marked with an "M" (like MisZionM, MisMachinesM, etc.). I was wondering if these files are ever played at some point. All I've heard in missions are the "L" and "H" ones.

MisMachinesM is the combat music in the One Zero and, I suppose, Zero One constructs (while the out-of-combat music there is MisMachinesL).

As of the others, I've never heard them in the game, and I don't know anybody who has.