The Guardian of Legacy was a group of old men who weren't bound by any kingdoms. Just like what their name was, they were guarding the legacy left by the First Master to ensure the safety of the next masters, generals, or even the advisers of White Army. They needed to make sure that all the aspects were satisfied before the army could be utilized to the fullest. They would also make sure that the army was not used to harm innocent people and still used to bring peace and balance to the mystic realm or astral world, or whatever human said it.
But, other than those duties, these old men's main job was to record the activity regarding White Army. They had their own records about the previous masters, even from the first master, and their own special traits. They even had noted down the rules set by the first master and the prophecy about the White Army. Everything related to the White Army, they knew it all.
But, even as old souls, they tended to forget something.