there's a billboard in Silver's story, the letters are kinda tough to read, but it's an ad for a movie Sonic Adventure games advertise called Chao in Space. Seeing as Sonic Adventure 1 and 2 have Chao in Space and Chao in Space 2, we can see the billboard is advertising a third movie, Chao in Space 3, so therefore, Sonic '06 is Sonic Adventure 3
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