From Sega Retro
Why did you take down the Sonic & Knuckles Collection credits? The credits for the game state that Setsumaru was the Sound Coordinatior, and the other three people only "Arranged" (aka MIDI-fied) the compositions.
Therefore, Setsumaru is the only one in the position to have composed those nine tracks.
While on the topic of Sonic 3 compositions, I think Sonic Jam is pretty dependable proof that Setsumaru composed the Data Select Screen music. I say this because the credit format for the game is the same as that of NiGHTS into dreams..., where there are instances of each sound team member only composing or only arranging a track in addition to handling both aspects. Christmas NiGHTs, then, continues this trend by using the same credit format in referencing past compositions, much like Sonic Jam does regarding the arrangement of Data Select Screen.
Lastly, the differences in Sonic Jam's music are, in my opinion, rather qualitative and rather easy to distinguish. A tropical style sound and instruments similar to Sonic 3's Data Select Screen music is heard for Sonic World's main theme (http://www.youtube.com/watch?v=Y_3ubAmadBs), and the composition between the two is also quite similar. Meanwhile, the music's high quality can be related to the rest of the Sonic Word half of the game as well as the game's opening and credits theme, thereby entitling Setsumaru to the top position of the game's "Compose & Arrange" credits by having the majority. Tokoi's more jazz-based sound appears in the Game Select half in tracks like Time Trials and Option/Digital Manual (http://www.youtube.com/watch?v=L1AUFNaLxVI), where the music sounds like it is of lower quality as opposed to the Sonic World half. Compare this to another Tokoi track from around that time to see what I mean: http://www.youtube.com/watch?v=nSzulrcb35g
[04/20/11] Concerning Setsumaru's supposedly uncredited role in Sonic 2, wouldn't that make him OYZ? That's the only sound assistant whose real name hasn't been found out yet, and Setsumaru so far does not have any super-deformed aliases [I don't think Setsu counts]. In the context of those credits, where all the other sound assistants had aliases, surely Setsumaru is represented. Who else can possibly be this "OYZ" fellow anyway? If Kubota can be Jimita and Sawada can be Dawasa, what's stopping Setsumaru from being OYZ?