From RWP Wiki
Scoreboards - referred to as leaderboards on Xbox 360 disc cases - are a list of the best scores (or similar ranking devices, like times) achieved while signed in to Xbox Live. Scoreboards are not cross-game: that is, how you rank on Kameo's scoreboards won't affect how you rank on Perfect Dark Zero's scoreboards. This independence of scoreboards also means that you won't appear on the Kameo scoreboards if you play Perfect Dark Zero.
Some games allow you to filter the scoreboard display to display only your Friends' scores, scores achieved within the last month, or scores achieved within the past week.