Sonic the Hedgehog 1 on the Genesis was released in the North American market first before any of the other regions. Sega of America really needed it to be released a few weeks before the North American launch of the Super Nintendo and Super Mario World. The EU and JP releases were much more polished overall and have more parallax in some stages and have a few more additional effects. Image related is an 8-page magazine ad for Sonic the Hedgehog 1. It was posted in the October 1991 issue of EGM and was party of the launch advertising. Weird off brand comic.

https://youtu.be/OHE94oBDVW0

https://youtu.be/mK0OFsWWzu4