Furthermore, it is said that the ken-suishi in the early period were not familiar with diplomatic courtesy and they visited China without the sovereign's message, which is questionable because Wa should have been very familiar with the social system, culture, or diplomatic courtesies in China from the longtime cultural exchange (the first ken-suishi was not described in "Nihonshoki" (Chronicles of Japan), was described only in Suishu (the Book of the Sui Dynasty), while ken-suishi was described as `kento-shi' (Japanese envoy to Tang Dynasty China) in the "Nihonshoki" (Chronicles of Japan).
また、倭は長い交流を通じて中国の社会制度・文化や外交儀礼に詳しいはずなのに、初期の遣隋使派遣では、ヤマト王権は外交儀礼に疎く、国書も持たず遣使したとされる（第1回遣隋使派遣は『日本書紀』に記載がなく『隋書』にあるのみ、また『日本書紀』では遣隋使のことが「遣唐使」となっている）。