It possible that the Library houses information on all life forms stored in Installation 04. When I played through The Library I noticed that as I progressed through the level that the colour of the wall decorations changed. The second flour was Red, third was Green, and the fourth was Orange. When I seen this I started to wounder, if these colours represented forerunner hierarchy or the New Didact, Since the new didact is a cross of Builder, Life Worker, and Warrior Servant. Builder being at the top of forerunner society hence why it is on the last flour of the Library. Life Worker being green and Warrior Servant being on the bottom.
I also believe that 343 Guilty Spark confuses John 117 for the Didact. The Didact did wear green ceremonially armor just before the collapse of the Forerunner capital.
I love halo so much for this reason! The fact that every level and map can contain information about the story if one uses there imagination and creative thinking.