We don't have concrete "proof", but I don't really think it's necessary when the US script is very obviously a revised version of the EU script. Why in the world would anyone in their right mind go back and make the script worse for the EU release?
Even if it turns out the US version was released first, it doesn't necessarily mean it's an older revision. The Legend of Zelda: The Minish Cap was released in Europe 8 days after the Japanese version, according to GameFAQs, yet the European version contains unique bugs that are not present in either the Japanese or US versions.
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