shots of the game actually showed that Sonic CD was  meant to be in the game, however most likely due to emulation  problems of the Sega Mega CD, and to the dismay of every Sonic fan  (people complained that Sonic Jam on the Saturn (another  compilation) should have had Sonic CD, however, it was impossible  due to the limited CD space), it was taken out of the final product.  Sonic CD later appeared on Sonic Gems Collection but it was a PC  version port.