The Gregorian calender (1874,etc.) was officially introduced in Japan in the year 1873, five years after the Meiji restoration. It has been in use sparingly since that date. To this day however, Japanese style dates (Heisei 25, etc.) are used on all coinage and all official documents. It is a misconception that the gregorian calender arrived with the post war occupation. But, on further inspection, and although it does mention Kyoto, I don't think this is of Japanese origin but of Chinese origin because in the written text on the sides of the page, next to the listed tables, there is not one example of hiragana or katakana (the japanese phonetic symbols) used to conjugate verbs. Also, too many of the Kanji are totally unknown here in Japan which is also typical of chinese texts.