Page 93 of this [0] source (cited in the article) appears to verify the topic of the article.
Certain Wikipedia authors finalize their articles in their sandbox and then copy it over, which was done in this case [1] with the sandbox including 180 edits and work over several weeks.
As introductory paragraphs are a summary of the article, they don't have to contain any citations [2], certain editors who only write long-form Wikipedia articles are fond of that style.
Entering "Koryos" in Google Scholar brings up more sources, no sources show up when using the diacritic.