The international Law of the Sea treaty, such as it is, allows you to extend your exclusive economic zone (the area where you have fishing and mineral rights) past 200 nautical miles, depending on if the sea bed extends from the land as a shelf or not. If new surveys show the sea bed, in areas that are otherwise not traversed (such as in this image) it's normal.
This is why, btw, China is building artificial islands everywhere.
The international Law of the Sea treaty, such as it is, allows you to extend your exclusive economic zone (the area where you have fishing and mineral rights) past 200 nautical miles, depending on if the sea bed extends from the land as a shelf or not. If new surveys show the sea bed, in areas that are otherwise not traversed (such as in this image) it's normal.
This is why, btw, China is building artificial islands everywhere.