Board Thread:Geometry Dash Gameplay Discussion/@comment-26533608-20161222141924/@comment-34844048-20161222183715

I believe you can't sync data to World unless you've logged in with your main game account for the first time, but if you were to refresh your account page then it'd be back to just your actual progress in GDW.

If the 50 Diamonds lock is a vault I'm guessing the keys unlock a secret shop with the door in the bottom right where you could buy more icons, but so far no confirmation on what it really is.