From Sonic Retro
Magazine Preview #06 - Sonic and Tails Spin Dashing in Prototype Casino Night Zone
|Source: GamePro||Source: Sonic 2 Beta ROM|
First of all the backgrounds are different. There're also some yellow squares which were placed straight up instead of rotated 45 degrees like the prototype we have. Finally, the dusts when doing Spin Dash suggest this pictures came from a newer prototype.