Japan claim that the sea between Korea and Japan is Sea of Japan but its actual name is East Sea.
East sea was used for more than 2000 years.
However due to Japan's colonial rule of Korea, the sea was called as Sea of Japan since then.
If you look for historical record of Korea, Japan, and China, it is easy to find out that the sea has been called as East Sea,
Also, IHO set East sea as correct mark.
For these reasons, East sea should be used officially.