There is no point submitting multiple scores to a leaderboard.
This is what the documentation says
The game services checks if this score is better than the player's current leaderboard entry for the daily, weekly, or all-time score. If it is, the game services updates the corresponding leaderboards with the new score.
Why do you want to submit multiple scores to one leaderboard ?
If you have different levels you can create different leaderboards for that.
Games can have multiple leaderboards, up to a maximum of 100. For example, a multi-level game might provide a different leaderboard for each level, and a racing game might have a separate leaderboard for each track.
Solution for your Comment
The game services sends a score report back to the game client. This report tells the client whether this is a new daily, weekly, or all-time high score. If it isn't, the game services will tell the client what the current daily, weekly, or all-time high score is for this player.