A new glimpse into Sega’s development history has been found: A previously unreleased prototype of Sonic The Hedgehog 2: http://hiddenpalace.org/Sonic_the_Hedgehog_2_(CENSOR_prototype)
There aren’t any drastic changes from the final release and most were small things like adding a signpost for a “save” area:
Some mistakes were found that made certain levels unbeatable, such as this platform which is rotating in the final version:
So, overall, nothing drastic, but still a fun glimpse into the development cycle of one of the most popular…and many people’s favorite Sonic game of all time.