In the following record, the governor of Gangwon Province asks King Sejong to allow him to populate Usan, which he described as being a fertile island with many products and having a diameter of fifty ri. He also said it was surrounded by cliffs, but had places to anchor.
Source:『世宗實錄』 卷 七十三, 世宗 十八年 閏六月 甲申條The island being described in the above record is almost certainly present-day Ulleungdo. The fact that it is described as "Muleungdo's Usan" suggests that Muleungdo was being used to refer to the island group and that Usan was the largest island in that group. This April 15, 1412 record also suggests that Usan ("Yusanguk-do") was the main island, and that a smaller neighboring island was called "Muleungdo." This would explain why Korean maps up until sometime in the 18th century showed Usando to the west of Ulleungdo, instead of the east, where Ulleungdo's neighboring islands are. For example, here is the famous 1530 map, which shows Usando (于山島) to the west of Ulleungdo.
June 19, 1436
江原道監司柳季聞啓 武陵島牛山 土沃多産 東西南北各五十餘里沿海四面 石壁周回 又有可泊船隻之處 請募民實之 仍置萬戶守令 實爲久長之策不允
강원도 감사 유계문(柳季聞)이 아뢰기를,“무릉도(武陵島)의 우산(牛山)은 토지가 비옥하고 산물도 많사오며, 동서남북이 각각 50여 리로 사면이 바다이며 석벽(石壁)으로 둘러싸여 있고, 또 선박이 정박할 만한 곳도 있사오니, 청컨대, 백성을 모집하여 이를 채우고, 인하여 만호수령(萬戶守令)을 두게 되면 실로 장구지책이 될 것입니다.” 라고 하였으나 윤허하지 아니하였다.
Gangwon Provincial Governor Yu Gye-mun said: "The land of Muleungdo's Usan is fertile and has many products. It is surrounded by the sea and is about 50 ri from both north to south and east to west. It is surrounded by rock cliffs, and there are also places where ships can anchor. Please allow me to gather people to settle this place. If we do this and assign a magistrate there, it will likely be a long-lasting endeavor." The request, however, was denied royal sanction.
Chosun officials seem to have taken the information in the April 15, 1412 record into account because according to this September 2, 1416 record, Kim In-u was made inspector of the "Mulueng Area", not "Mu-leung Island." Also, even though the record says that Kim In-u was sent to the "Muleung area," this February 5, 1417 record says that he returned from "Usando" with local products that included large bamboo, seal skins, raw ramie cloth, silk wool, and geombak trees (or wood). This suggests that the people that Kim In-u met on his trip told him that the name of their island was "Usando." After Kim In-u's return from "Usando," as mentioned in the February 5 report, the "Muleung area" began to be referred to as "Usan-Muleung," as this February 8, 1417 record shows:
Notice that in the above quotes, "Usan" comes before "Muleung," which suggests that it was the bigger island.
Minister Han Sang-gyeong told the six government authorities and the Daegan to discuss the best ways to evict the Usan-Muleung residents....
The appropriate thing to do is to keep Kim In-u as the area inspector, and send him back to the Usan-Muleung area to bring its residents to the mainland....
Also, an August 6, 1417 record reported Japanese pirates at "Usan/Muleung," and an August 8 1425 record said that Kim In-u was made Inspector of the "Usan-Muleung Area." However, even with all the references to the "Usan-Muleung area," there still seemed to have been a tendency to use "Muleungdo" to refer to the island group as this October 20, 1425 record and the above June 19, 1436 record suggest.
I believe that at the time of the above record, Ulleungdo was being called "Usando," and its neighboring island, Jukdo, was being called "Muleungdo." However, I think that "Muleungdo" was also used to refer to the island group (Ulleungdo and its neighboring ilsands). There is still no evidence that either Muleungdo or Usando was referring to Dokdo/Takeshima, which is ninety-two kilometers southeast of Ulleungdo. On the contrary, all the evidence suggests that Muleungdo and Usando were neighboring islands that were close enough to each other to cause name confusion.