In 1694, the Korean government sent Jang Han-sang (張漢相) to inspect Ulleungdo. In his inspection report, he wrote the following:
The small island five ri (two kilometers) to east of Ulleungdo, which was described as having haejang bamboo (海長竹) growing thickly on one side, was almost certainly Ulleungdo's neighboring island of Jukdo (竹島) because Jukdo is two kilometers off Ulleungdo's east shore and is Ulleungdo's largest neighboring island. The island was labeled as "Usando" (于山島) on Bak Jang-sang's 1711 inspection map of Ulleungdo.
About five ri to the east is one small island. It is not very big or very high, and it has a grove of haejang bamboo (海長竹) growing thickly on one side. On a day the rain clouds cleared and the fog settled, we went into the mountains and climbed the central peak. Two tall mountains to the north and south were facing us. This was the so-called Sambong (三峯 - "Three Peaks"). The winding shape of Daegwanryeon (大關嶺 - mountain range on the east coast of the Korean peninsula) was visible to the west. Looking toward the east, there was one island far off to the southeast. The size was only about one-third of Ulleungdo. It was only about 300 ri [120 kilometers] away.
東方五里許 有一小島 不甚高大 海長竹叢生於一面 霽雨?捲之日 入山登中峯 則南北兩峯 岌崇相面 此所謂三峯也 西望大關嶺逶迤之狀 東望海中有一島 杳在辰方 而其大滿蔚島三分之一 不過三百餘里.
The island that Jang Han-sang described as being far off to the southeast of Ulleungdo, about 300 ri away (120 kilometers), was almost certainly Liancourt Rocks (Dokdo/Takeshima), which are about 90 kilometers southeast of Ulleungdo. Inspector Jang described the rocks as being about one third the size of Ulleungdo, which tells us he did not travel to the rocks because Liancourt Rocks are actually only about 1/390th the size of Ulleungdo. Later, in the conclusion of his report, Inspection Jang seems to refer to the island as being Japanese territory. Here is the quote:
The above quote is my corrected translation of the mistranslation I was referring to above. It was in the conclusion of Inspector Jang's 1694 report. The "distant, hazy, inconspicuous island" was almost certainly referring back to the distant island referred to earlier in the report as being about 300 ri (120 kilometers) to the southeast of Ulleungdo. The fact that he reported seeing the island while looking at Japanese territory suggests that he believed the island to be Japanese.
If one climbs a mountain peak on the island (登島山峰) and looks carefully (審望) at that country's (Japan's) territory (彼國之域), there is a distant, hazy (則杳茫), inconspicuous island (無眼杓之島). Its distance (其遠近) is unknown (未知幾許).
Also, in a 1714 Korean report, an island visible to the east of Ulleungdo was described as being on the Japanese border, which suggests, again, that they believed the island to be Japanese:
I listened carefully to the people in the ports (浦人) who said, "Pyeonghae (平海) and Uljin (蔚珍) are closest to Ulleungdo, and there are no obstructions along the sea route. Visible to the east of Ulleung is an island that is on the border of Japan." In 1708 and 1712, strange-looking ships drifted to the borders of Goseong (高城) and Ganseong (杆城), so we know that Japanese ships frequently come and go. The government, however, says that the vast sea is a barrier, so there is no need to worry, but how can we be sure that a future war will not break out in the Yeongdong region instead of the Yeongnam region? We cannot allow even a little delay in taking measures to be thoroughly prepared.
In accordance with the request, the Myodang (廟堂) requested that Gangwondo be reprimanded to cracked down on its military officials.
辛酉江原道御使趙錫命 論嶺東海防疎虞狀略曰 詳聞浦人言 平海蔚珍 距鬱陵島最近 船路無少礙 鬱陵之東 島嶼相望 接于倭境. 戊子壬辰 異攘帆穡 漂到高杆境 倭船往來之頻數 可知. 朝家雖以嶺海之限隔 謂無可憂 而安知異日生釁之必由嶺南 而不由嶺東乎. 綢繆之策 不容少緩. 廟堂請依其言 飭江原道 團束軍保.