In another thread on the issue there were a couple of interpretations of how this could make sense. One was that the new men added to the unit 'inherited' the arms and armor of its fallen members. The less grisly option is that the general of the unit is responsible for providing the weapons and armor to his men, so he has access to the better equipment and distributes it to the newcomers. Thus the new troops can have a legitimate reason to receive these bonuses even though their valor must be earned individually on the field of battle.

Ajax