Have to agree with the fellas above. Don't sweat it. I work for a video game company and am involved in quite a few of the product naming cycles, and the hardest thing we come across is finding a name that hasn't been used before. I'm sure there's a game with my dio name "Disciple" out there. You can bet there's a "Retaliation" and a "Terror" as well.
Now, if you'd named yours "Rainbow Six" there would be an issue.