This article deals with three controversial issues concerning the chongniu 重纽 or doublets of Middle Chinese rhyme tables. They include (1) the definition of chongniu, (2) the classification of the chongniu rhymes with alveolar and dental initials, and (3) the inclusion of geng 庚 and qing 淸 rhymes in the chongniu. Based upon a careful observation on the Middle Sino-Korean Korean pronunciations written in the Hunmong jahoe 『訓蒙字會』, compiled by Choe Sejin (1527), this article claims that (1) the difference between chongniu A and B is not main vowel but glide, (2) the chongniu rhymes with alveolar and dental initials can be classified as chongniu A in terms of phonetic similarities, and (3) the geng 庚 and qing 淸 rhymes can be included as chongniu rhymes as well.