Didn't they add a new CD to the Gorosei? Was he also alive during the Void Century? If so I wonder how many CDs are that old.
I wonder what made Dragon leave the marines and fight the WG. Did he come across poneglyphs or just see the WG/CDs doing fucked up stuff. He has the sky island-style markings on him, so maybe he learnt from them? Maybe he met them, they told him the truth but then he had to do a buster call on that sky island (is this even possible?) but he regretted it and got tattooed. Or maybe they told him, the marines were listening in without him realising and then he couldn't stop the buster call, so they told him to carry on their will and tattooed him.