Yes, I have the same reference book. My translation is basically the same as the one above. This window marking has been discussed on several online sites. Most agree that it seems to represent an arsenal sub-contractor who makes replacement parts for reworking/ replacement. Perhaps after original production has ended and existing inventory is depleted?
There is additional info on this Forum under; Russia, (page 2), 6X4 with “window” on scabbard. viewtopic.php?t=114 Thanks, Mike