The enterprising governor of Tsushima was empowered by the Chosôn court to issue access permits to Japanese envoys wishing to trade with Chosôn, according to historian Kenneth R. Robinson of International Christian University in Tokyo, who published an article on "The Tsushima Governor and Regulation of Japanese Access to Chosôn in the Fifteenth and Sixteenth Centuries" in Korean Studies 20 (1996): 23-50.
This article suggests that Chosôn government officials did not strictly adhere to the tributary system model of international relations in their dealings with Japanese. Officials borrowed from Chinese example and from domestic policy in designing Japanese access control policies that responded flexibly to political conditions in Japan. The munin access permits issued by the Tsushima shugo ['provincial governor'] were perhaps the most important feature of these policies. But treatment of Tsushima and the Tsushima shugo by Korean officials made ambiguous the identities not only of Tsushima and the Tsushima shugo, but also the state boundaries of Chosôn and Japan. These negotiable ambiguities raise questions of how to conceptualize relations between Koreans and Japanese in the fifteenth and sixteenth centuries....Apparently, a fair number of these envoys were imposters, according to the abstract of a 1997 paper by Robinson presented at the Association for Asian Studies annual meeting entitled "Japanese Imposter Sovereign Envoys to Choson: The Late Fifteenth Century."
The munin systems of access control, in which Japanese bound for Chosôn obtained a munin (access permit) from the Tsushima shugo, did not originate directly from the tributary system of international relations [that prevailed in China]. Adapted from Chosôn government policies for controlling the domestic travel of Koreans, the munin systems served the complementary needs of the Chosôn government in regulating Japanese contact and of Sô Sadamori and his successors as Tsushima shugo in enhancing the powers of that office. The Tsushima shugo issued three types of access permits to three types of Japanese for three distinct activities: to envoys for diplomacy, which was understood generally to be a fiction for trade; to Tsushima islanders trading in fish and salt along the Chosôn coast; and to Tsushima fisherman for fishing in Chosôn waters. In the space between the vision offered by international relations in the tributary system model and the complexities of policymaking that faced Chosôn government officials, Muromachi Bakufu officials, and the Tsushima and other provincial governors there emerged policies that made ambiguous the administrative boundaries of "Chosôn" and "Japan" and the identity of "Tsushima."
Royal envoys from Ryukyu, envoys of Japanese provincial governors and traders, and Japanese shogunal envoys began visiting Choson Korea in the late 1300s and early 1400s. In the late fifteenth century, Japanese impostor sovereign envoys began seeking to trade with the Choson government. They donned a variety of disguises, modeling themselves after envoys with whom the Choson court had been trading for decades. Some represented the "King of Ryukyu," others the rulers of countries unknown to Korean officials. Choson court officials met (impostor) Ryukyu envoys as they had earlier royal envoys until they began to recognize mistakes in the envoys' documentation. These less fortunate envoys were received at a reduced level of reception, one reserved for foreign government elites. As for the envoys of the rulers of the unknown countries, they failed to convince Korean officials of the existence of those countries. But, rather than turn away these visitors, Choson court officials received them at the same, reduced status as the unmasked impostor Ryukyu royal envoys. Reception of these impostor envoys displays elements of the Choson Korea world order. Formed in part to promote trading over raiding, this hierarchical world order functioned simultaneously with the Ming Chinese tributary system. Choson court officials ranked the Chinese emperor as superior, the rulers of the tributary states of Japan and Ryukyu as equals to the Choson king, and Japanese and Ryukyuan government officials and traders as of lower status. The tributary system informed the structure of the Choson court's reception system, but tributary status did not confine Choson court officials to a set portfolio of foreign policies. Stated differently, Korean officials did not defer to the Chinese in their conduct of relations with Japanese and Ryukyuans.The position of Tsushima seems a good deal less ambiguous than it was 500 years ago, but the general nature of international diplomacy doesn't seem to have changed all that much, regardless of the polite fictions enshrined in the Treaty of Westphalia (at which England, Poland, Muscovy, and Turkey were the only European powers that were not represented).