unless you have a strong reason to begin formal marketing early, there is no reason not to stay with a code name until you have a press pack ready, which for new games with low/no advertising budgets is usually about a month before release (even if the release is a good demo, and not the full sellable product)
Typically, you need the formal name for marketing purposes. anyone tracking it will be fine tracking via the code name. But once you start hitting large audiences, then you need a name to be stabilized so people can refer to it easily and find it.
Typically you don't want to start bothering press/magazines/game review sites until you have a demo ready for them to try anyway. Text emails, even video's alone don't tend to excite the reporters. That is just what you are telling them. Especially for new groups, it doesn't matter what you say it is like, its your baby, its the best thing in the world. They want to see and play the game. If its not ready for audiences, at least in demo form, no game review source is going to want to post anything about it. And also, they receive tens to hundred of leads on fresh games a day easy. Even if they like your product, if it's not ready for some form of distribution, they won't post it, and when you talk to them again a month later when your demo is ready, it will be almost as if you never spoke in the first place. I.e. so many games have passed in front of them since, that it will be difficult to recall.
Naturally, all the rules change if you are a game giant like Blizzard. Game reviewers want to leak information on that as soon as possible. even years before release, because enough people want to hear about it.
So, key concept, is that you don't need to switch from code name to formal name until you are ready for marketing.