It's only good up to a certain point. If a pokemon passes legal, it's 'legal' - it hasn't been proven to be 'legitimate'. To be proven legitimate, you'd need to get someone who has knowledge of the pokemon's inner data to check it. Like, hex values, GBA algorithms (proper ones), etc. =/ I don't know how to explain it, legal isn't a checker for legitimacy, it's a checker for legality, which are two different things. Legal means that the pokemon has the right movesets/EV combinations, everything basic, but it doesn't prove that the pokemon wasn't created by an AR or pokesav, etc =/ only that it -looks- legit.