In case no one has caught on, all of this is available on Emuparadise. Funny enough, it appears they do know what a beta is. Take a look at this Garfield scan (together with a photo of the lost viking level). You'll notice they explain what a beta is at the bottom left of the page. I think they probably did just superimpose their own pic onto a blank screen that Sega hadn't filled with graphics yet. If you look throughout the issue and others you'll see that all of their previews have a titlescreen shot that notes the system, system bits, and region. If the proto came with nothing discernible on the title, it makes sense they'd come up with something in order to avoid breaking tradition. After all, Sega wasn't so technically inept with new gen hardware at this point that they wouldn't be able to provide a properly colored Knuckles pic. It's probably just their own mock-up. It may have been an earlier time, but lets not assume they weren't capable of knowing a thing or two.