I have a question.
While this xp gain is based on a soldier not dying, what are the odds my soldiers will not die through an unlucky event, assuming I don't simply reload when I loose a soldier.
If the odds are high that a soldier will die before completing 100 missions, then I would expect either training to be easier, or alternativly, a way to get new soldiers who already have some xp, to reflect the national armies experience against the aliens providing a more skilled baseline of troop than the initial start.
I would expect that xp to be less than a surviving soldiers xp of course, but I would also expect there to have been some xp gained by a soldier.