I believe revision is the correct term for us to use, even if Sega used the "version" terminology. Revision is usually used for lesser changes that don't warrant being called a major overhaul, and version is used for major changes. For example, I would consider the engines found in each successive game to be new versions, as there were major changes and rewrites. But, within each game, there are the different revisions, which aren't enough to denote a major version. But, that's just my opinion. I'll still be calling it revision no matter what you guys do - it's not too hard to tell what someone's talking about.