<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by JohnAx:
I've never officially asked, but just as your first-class ticket comes out of D inventory when nothing better is available, I'd be pretty sure they'll do the same for coach.</font>
The only exception is booking AY over the atlantic, you can book in J. Otherwise, you are correct, you will book in M or D.