The date of hotosho was written as the 4th year of Keio era, but by the edict of the practice of assigning one era name to the reign of each emperor, it was changed to the first year of Meiji era, back in January 1 (different from changing the name of an era after Taisho).
奉答書の日付が「慶応四年」となっているが、後の一世一元の詔により慶応四年は1月1日(旧暦)に遡って明治元年に改められた（大正以降の改元とは異なるので要注意）。