In all probability, there are many thousands of privately printed post cards created with no comprehensive catalogue that could record every issue. That being said there are many very interesting cards from both a design and postal history perspective. Four examples are included for reference with estimated issue dates all within the first quarter of the 20th century. A fascinating area of collection!
Special cancellations were generally introduced in the late 19th century in Japan. Sheetlets were another interesting form of recording travel locations. Two of the postcards above have special cancellations and for viewer interest a set of private sheetlets is included below. The commemorative stamp is the Manchukuo Emperor's visit to Japan 1935.4.2 1.1/2s and in one case the 3s. 10 sheetlets trace a series of visits to different locations in Japan during the period from 5th April to 3rd May 1935 (Showa 10 in the Japanese calendar)