User blog comment:ThatGuySonic/Sonic Timeline Placement/@comment-4606132-20120218194151

it think that for generations they mostly went with things from the "main-series" in the story, the main-series being the games represented in the game (even though sonic does refer to Secret Rings) because tails has bin in green hill zone in games other then sonic 1, so the only green hill they consider canon is the one from sonic 1, i guess