It's frustrating for achievement hunters when there is a post-launch update which adds more achievements. Having all of a game's achievements on launch isn’t considered a “Perfect Game” / “100% complete” anymore. Likewise, if a game adds achievements tied to DLC, your only way to get 100% again is to buy the DLC.

Even if it isn't called a "Perfect Game" anymore, there should be a similar distinction to recognize a user's efforts.