At the March OGCA (Columbus, OH) show I examined a Model 38 Arisaka, both government (concentric circle stamp) and school marked (1/X). The serial number was preceded by two zeros and three characters and numbers had been stamped on the chamber top.
The "zeros" indicate an arsenal rebuild and the faint serial number and smooth blue-brown metal finish indicates refinished metal. What was interesting is that on a close look in good light you could see filing (?) flats on the chamber to barrel slope and on the receiver edges! Apparently when the rifle was refurbished some file work was necessary to prepare the rifle for the reblueing process. While not readily noticeable, it is surprising that this work passed inspection.