I remember this was discussed once before, but I don't remember what conclusions were reached and I'm too lazy to look up the posts. Personally, I think that during TFL the Light forces had been fighting (and losing) for decades, so The Legion could have been a reference to a specific unit in a rather ragtag army. By the time of SoulBlighter, the west had had decades to stabilize and rebuild, so a more formal army consisting of multiple legions could have developed.
"...and their right hands were raised in menace against mankind." sieg zeon
