I noticed that today, also, and I cannot find any mention of a sixth one online, yet. UPDATE: I found this on another thread "The Assembly Chamber is a place where you can combine shards, head to the Jedi Temple. Once you exit the elevator take a right and walk into the instance, it's like your own personal workshop. As you get close to the matrix the codex will unlock as datacron 6." Update 2: I just tried this and my codex did not update. Update 3: It worked, but I don't know if it was me leaving the area that made it update or clicking away from Coruscant and then back to in the codex.