If 'A Serpent's Lust' was written in 1767, a year before the preface was written, and one takes into consideration the year 1767, which had a leap ninth month, these dates in the work become coherent.
もし、序に書かれた年の前年の明和4年に「蛇性の婬」が書かれたとする場合、序の年の前年、閏9月のあった明和4年を念頭におくと、うまく計算が合う。