About a month after King Sejong sent Lee An-gyeong to Kangwon Province to visit Yodo (see here), the king sent a message to the governor of Hamgil Province (in the northeastern part of Korea) to send to him a man named Kim Nam-ryeon, who was reported to have knowledge of Yodo. If the man was too old to travel, the king told the governor that he could interview the man and send a report, instead. The following is the record of the king's instructions to the governor of Hamgil Province:
Notice that King Sejong had ordered a search for all the people who had knowledge of the island, "Yodo," which shows he had a great interest in finding the island. It is not mentioned how many people the king was able to find, but the above record shows that he found, at least, one person who was reported to have been to the island. Since the above record was made one month after Lee An-gyeong was ordered to "visit Yodo," it appears that Lee was unable to find the island, which prompted King Sejong to start looking for people with knowledge of it.
Source: 『世宗實錄』 卷 四十七, 世宗 十二年 一月 丁卯條
January 26, 1430
奉常寺尹李安敬 訪問蓼島而還 傳旨咸吉道監司 前此往見蓼島之人 及素見聞本島之狀者 悉訪之 咸興府蒲靑社金南連 會往還本島 其給傳以送 若老病 則詳問本島形狀及人居殘盛 衣服言語飮食之類 以啓.
봉상시윤(奉常寺尹) 이안경(李安敬)이 요도(蓼島)를 방문하고 돌아온 건에 대하여 함길도 감사에게 전지하기를, "과거 요도(蓼島)에 가본 적이 있는 사람이나, 이 섬의 상황을 전부터 보고 들은 사람을 모두 찾게 하니, 함흥부(咸興府) 포청사(蒲靑社)에 사는 김남련(金南連)이란 사람이 일찍이 이 섬에 갔다가 돌아왔다고 하므로, 그 사람을 보내도록 하되, 만약 늙고 병들었거든 이 섬의 생김새와 주민들의 생활은 어려운지 넉넉한지, 의복·언어·음식 등의 사정은 어떠한지 그 사람에게 자세히 물어서 아뢰라." 하였다.
The following instructions from the king were sent to the governor of Hamgil Province concerning the visit to Yodo of Bongsangsi Official Lee An-gyeong: "Having ordered a search for all the people who have either been to Yodo or who have heard about the island, it is reported that there is a man named Kim Nam-ryeon, who lives in Pocheongsa in Hamheungbu, who has been to the island. You can send the man, or if he is too old and feeble, you can thoroughly interview him about the features of island and about its inhabitants, including whether their lives are difficult or not and about their clothing, language, and food, and send a report, instead."
There is no record of how King Sejong came to hear of Yodo, but, judging from the above record, he assumed that people were were living on the island. The record shows King Sejong was quite interested in finding the island, but even with all of his interest and efforts, he never found Yodo or any other island in the East Sea (Sea of Japan).