After Keichu advocated that the Manyoshu was initially completed in 16 volumes, and that volume 17 to 20 were added later to create a second version, there have been various opinions about the matter; there is a great deal of evidence to support the opinion that the Manyoshu was divided at volume 16, including that the table of contents goes up to volume 15 in old manuscripts like 'Genryaku Kohon' (revised version in Genryaku era) and 'Amagasaki-bon' (manuscript of Manyoshu found in Amagasaki), the citation of earlier sources, and the categorization by Budate.
契沖が万葉集は巻1～16で一度完成し、その後巻17～20が増補されたという万葉集二度撰説を唱えて以来、この問題に関しては数多くの議論がなされてきたが、巻15までしか目録が存在しない古写本（「元暦校本」「尼崎本」等）の存在や先行資料の引用の仕方、部立による分類の有無など、万葉集が巻16を境に分かれるという考え方を支持する証拠は多い。