Board Thread:General Discussion/@comment-1031724-20160828014723/@comment-24412830-20160902015541

Mystic Monkey wrote: I think all the games share a same continuity, just not in specific order of time. South Island and West Side Island from Sonic 1 and 2 are on the same world seen in Sonic Unleashed just Sonic had no reason to go there.

And Sonic Generations mentions in Knuckles profile that he is still guardian of Angel Island.

The only games excused from the continuity are Mean Bean Machine, Spinball and any game with Mario in it. Well Mario and Sonic is obviously Non-Canon to both their franchises.