Oda famously came up with the idea of the Supernovas on the spot after one of his editors said that Sabaody wasn't interesting enough, and it's incredible how easily he justifies their existence on the archipelago. It's established that Luffy doesn't pay attention to the news so he's not going to know about all these potential rivals, and the various routes of the Grand Line were mentioned back on Reverse Mountain when the crew got the log pose. Oda really has made up a world that gives him the freedom to do whatever he wants whenever he wants to, and that flexibility has served the series well over the course of its run.












