The Sonic the Hedgehog 2 "pre-beta" prototype is a prototype build of Sonic the Hedgehog 2 for the Sega Mega Drive. The EPROMs it was contained on claim it to be a "pre-beta" dated September 14, 1992.
To the untrained eye this version of Sonic 2 could be passed off as the final game, with every level being accounted for and all but the final three (Sky Chase Zone, Wing Fortress Zone (known here as Sky Fortress Zone) and Death Egg Zone) being completable. However, the Special Stages and 2-player mode have yet to be implemented properly, and there are a number of minor differences and layout changes, particularly towards the end of the game. It also lacks much of the polish seen in prototypes from here on out, such as title and score cards, introductions and endings.
It is possible this build was used when creating screenshots for the US manual for Sonic 2, and was the one photographed or recorded for a number of gaming publications around late September and early October 1992.