My two cents:
NM as a wiring method (cable, no conductors!) is not to be "mixed" with other methods. i.e. don't run in EMT. Overheating is the problem. And isn't that the main factor in many of the NEC 70 art.'s.
As for what NM is: most of the conductors are not marked; NEC 336 indicates that it is a 60 degree cable assembly. One piece that I have did have conductor marking: "TW" (60 deg. conductor, what do you know!).
