I\'ve read that Game Center Leaderboard scores are only updated when the newly posted score is greater than the already existing score.
This made me wonder if it is
You can choose low to high or high to low leaderbord type in iTunes Connect.
And you can always send any value to Game Center server, it's just that it will not save it unless it's higher* than the current score.
* if it's a low to high leaderboard, the value that is lower is actually counted as a higher score.