It was regarded as noteworthy and subject of discussion yet again in recent years that Hondo-ji Temple, which had been closely associated with the Chiba clan since the time of its foundation in late Kamakura period, kept its history record and it contains an entry stating Tanetsuna's age of death as 31; thus it was concluded that the age of Tanetsuna's death was incorrectly cited as "21" (May 28 koshijo, 1228) when "Azuma Kagami" was compiled referring the original historical materials, and the editors of "Chiba Taikeizu" believed the information on Azuma Kagami and made a "correction" accordingly.
ところが、近年になって鎌倉時代後期の創建であるとは言え、創建当時から千葉氏と密接なつながりを有した本土寺の過去帳に胤綱の享年を31とする記述があることが問題視され、『吾妻鏡』が編纂された時に原史料からの引用を誤って「年二十一」（安貞2年5月28日庚子条）としてしまったものを更に『千葉大系図』の編者が信じて引用して、これに合わせる形で"修正"を行ったものと考えられるようになった。