Here is a map called "満韓新図" (new map of Manchuria and Korea) which was included in a book "日露戦争実記" (a record of Russo-Japanese war).
The map was made on February 20th 1904, about one year before the incorporation of Liancourt rocks.
Liancourt rocks were indicated as Matsushima, the old name of the island.
You can see the borderline* between Ulleungdo and Matsushima (Liancourt rocks), which means that Japan already recognised Liancourt rocks to be out of Korean territory before the incorporation.
Korean government used to claim that Japan robbed Dokdo from Korea but it was not true.
(Please click the map to enlarge)
*The legend at the right lower corner mentions that this line is " 国界" (national border).