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I've been playing through Emerald for the past couple of weeks, trying to complete my Pokédex as I go so I can get a Johto starter from Birch. I think this is as much as you can possibly fill it pre-Hall of Fame without trading - once I've become champion I can pick up Anorith and Beldum as well as catch Latios/Kyogre/Groudon, then I'll trade over the last few entries from Ruby.
Logically it should have data for Metang because Steven uses one when you partner up with him against Team Magma, but I guess no one at Game Freak considered that. Not that it really matters anyway.