PHILIPPINES JAPANESE OCCUPATION HANDSTAMPED "K.P." OFFICIAL BUSINESS ON SCOTT N4

This is a scarce example of Philippine Japanese Occupation 5-centavos Provisional Regular Issue, First Overprinting (thick top bar), Scott N4, issued September 1, 1942, with a handstamped violet "K.P." and Japanese "Koyo" for Official Business mail.

Although Eugene A. Garrett's book, "A Postal History of the Japanese Occupation of the Philippines, 1942-1945", shows many examples of handstamped "K.P." and "O.B." markings applied during the occupation, it is unclear to me which office may have applied this handstamp.  I welcome suggestions.  Still, an interesting and scarce stamp.