the flower was called the mum, it represented the emperor of japan like a blessing. United States soldiers were asked to remove the mums and japanese soldiers removed them pre-surrender so the rifle could be surrendered in away not to dishonor the emperor. After ww2 the united states still needed the emperor to maintain order, prevent panic and enforce social cohesion in japanA lot of these were imported with either one hole or two holes side by side already in them.
The grind mark was done while these were still in japan. Cant remember what the flower/emblem was called but very few actually made it out with the flower still on them. Something to do with honor or something like that. Im sure someone more knowledgeable will chime in
I did not know about the hole in the receiver for no useful reason, that's unusual