User blog:Dettles/Admiral's names

So we know that when a marine becomes an admiral they get a code name but why? Up until Fujitora was mentioned I thought that Aokiji, Kizaru, and Akainu were the admirals and when someone new came along they would take the name of the one who was leaving. So if each admiral gets his own code name what was Sengoku's ( Going by my thought process I thought he was Kizaru because he in his devil fruit glowed gold.) And why the code names altogether?