Yes it looks like a build was done before the final release.

Hear it here:
http://www.youtube.com/watch?v=UkhjBAYL2Hs

It's 5 minutes so hear at them from start to end they will refer to at least 3 prototypes, but no footage. :(

Later today, thou, I will post here more Sonic1 footage of the prototype.
And yeah the Shadow of Atlantis footage will come too. 
Source: SEGA VHS promotion tapes.