Level's Diamond Goal: 5
Visible Diamonds in Level: 3
These levels usually have a cap on how many Diamonds can be in the level at the same time. In order to get more Diamonds to appear, you must first collect all the ones in the level. Then new Diamonds will start falling into the level along with regular blocks!
In these levels it is best to try and collect the Diamonds as fast as possible, so new Diamonds have a chance to appear.