In 1543, a Spanish vessel reported discovering three islands at a north latitude of around 25 degrees. These islands are believed to be the Kazan Islands. (Ref. 1, 2)
 
In 1639, a Dutch vessel reported the discovery of two islands around 26 degrees north latitude and 137 degrees east longitude. These islands are believed to be Chichijima and Hahajima. (Ref. 1, 2)

Together with the publication of a book titled Tatsumi Muninjima-Ki (A Record of the Munin (Uninhabited) Islands in the Southeast), a story was propagated in the first half of the 18^th century that the islands had been discovered in 1593 by Ogasawara Sadayori, lord of a castle at Fukashi in Shinano Province, who had erected a marker pole giving them the name of Ogasawara-tou. However, this story had no historical credence, and the person who had propagated the story, claiming to be a descendant of Sadayori was subsequently subjected to punishment. (Ref. 1, 2, 3)