An Yong-bok, a resident of Dongrae in Gyeongsang Province, went to Ulsan to visit his sick mother. There he met the monk Noi-hyeon and others, who he told about his trip to Ulleungdo, which he said was an island with an abundance of products. Noi-hyeon and his party listened to the story and decided to go to Ulleungdo with Yeonghae resident Yu Il-bu and his party.
Let's note visiting Ulleungdo was illegal in those days.
Many Japanese ships were at the island, and the people in the party were afraid to approach them, but An Yong-bok yelled in a thundering voice, “Ulleungdo is our territory. What are you Japanese doing crossing over our border? I am going to capture you.”
Japanese record shows that there weren't many ships, and Japanese fishermen were supposed to have rifles with them to hunt abalone.
At this the Japanese answered, “We are residents of Matsushima (松島) and come here sometimes to catch fish. That is all. We were just getting ready to return.”
Then An Yong-bok said, Matsushima is Jasando (Usando), which is also our country’s land. How can you be living there?”
This is the part on which Korean side base its claim. Matsushima is Jasando.
They claims that since "Matsuhima" is Dokdo/takeshima, Jasando is Dokdo/takeshima.
Note that Ahn's "Matushima" is the island where people could live, but you can not live on Dokdo/Takeshima.
The next morning they got in their boat and sailed to Jasando, where they found Japanese boiling fish in a big pot. An Yong-bok hit the pot with a stick and broke it and yelled at them in a loud voice. The Japanese gathered their pots together loaded them on their boat and ran away. Then An Yong-bok and his party got in their boat and chased after them, but they met a wind and drifted to Oki Island. The head of Oki Island came and asked why they had come there.
There were 21 Japanese and 11 Koreans according to Japanese record , but you can not fight like this at Dokdo/takshima.
Keep in mind Japanese fishermen had rifles with them to hunt abalone.
And it takes one day to reach Dokdo from Ulleungdo. Ahn started sailing in the morning and suppose they reached the Jasando in the evening; still, it is much short of one day.
[An said] said, “Last year when I came here, there is a letter written by the Gwanbaek (觀白 - an aide to the shogun) saying that both Ulleungdo and Jasando are Joseon territory. But the promise has not been completely kept. Why are you now again trespassing? Please relay this to Houki.”
The head of Oki Island said he comunicated this to Houki, but even after a long time there was no answer. He got angry, got on his boat, and headed to Houki.
Japanese record show no such letter.
According to Japanese record, it is written that An said from chosun to Ulleungdo was 30 Korean ri, from Ulleungdo to "Matsuhima" is 50 ri.
"Chosun-Ulleungdo = 30 Korean ri =120km"
"Ulleungdo - Matsuhima = 50 Korean ri = 200km
Chosun - Ullengdo =130km
Ulleungdo-Dokdo = 87,4 km
Ulleungdo-Oki ≦ ８７．４＋１５７．５≒２４５ｋｍ
Oki is much reasonable candidate for "Matsuhima" in this case.
In the previouse testimoniesto Korean authority , An's "Matsuhima" is most likely to be Jukdo, juding from the time it took from Ulleungdo, and the way people cook and fought. In Japaese record, An's "Matsuhima" is most likely to be Oki.
He said in another place the island was quite big. There are no island except Oki as
big as, bigger than Ulleungdo.
In either case, Ahn's "Matsuhima" is not Dokdo.
As a side note, Ahn wanted to find the island because he heard the island was rich in resouce. That was the island he wanted to go, to such an entent that he violated the law. And he wanted to avoid the death penalty after he was handed over to Korean authority. You know what some people would say to avoid the death penalty.