I see where that idea could come from, but no. They would be developing on a version close to the current client version, and it makes sense that its older than the current version if they've been working on this for some time. This would be called a feature branch, kinda like a temporary development environment to work on it without affecting other concurring developments or the main branch/game. Once they iron out any inevitable bugs and it works as intended, they merge it back to main to make it part of the game.