The highest seismic number is the earthquake event. The precursors are just that, precursors. They are not always present, especially in the case where something under the earth just snaps from whatever pressures are at hand. The quakes with a lot of precursors is like an avalanche just beginning to break traction and gather momentum. Events after the highest number are technically aftershocks due to reverberation and settling. An aftershock can reach a number as high as the original event but they are still considered to be aftershocks because it was the main event which precipitated them.