The purpose of this paper is to examine the characteristics of the additions of sounds as a product of changing North Korean linguistic norms reflected in Korean and grammar textbooks. The writing of Saisiot from the Enlightenment period to the Japanese colonial period have been a topic of frequent discussion. The publication of “The Theory of Korean” in the Enlightenment period established the Hangeul writing system, so writings produced using various writing systems were found in contemporary textbooks. “A Proposal for a Unified Korean Spelling System” was later published by the Japanese Government-General of Korea, but Korean spoken in North Korea has changed since the national liberation from Japanese colonial rule. Today’s North Korean grammar textbooks differentiate between the addition of ㄴand ㄷ. These additions are known as the Saisori phenomenon. After liberation, “jeoleumbu(絶音符)” or “saipyo(’)” were written between compound words, but this is no longer the case. This difference is one example of how Korean in North and South Korea differs with regard to the Saisori phenomenon, which is known as the addition of sound, and the writing of Saisiot. This study analyzed North Korean and grammar textbooks to determine how North Korean linguistic norms have changed over time.