I haven't seen anyone ask so I guess I have to do it. In Sun and Moon plenty of Pokemon in the game were not in the dex. Considering we know for a fact Mew is in the game but not spotted in the dex so far. Would it be unreasonable to assume that not all pokemon available in SwSh are in the leaked dex? No way Gamefreak is putting in 600+ but we may get into the 500s.