Couldn't make much out on two of the sticker photos. FWIW, aside from any serial number/mfr stamps, any numbers on the stickers aren't likely to be all that helpful? I think. I mean, unless somebody can look at the Saitama Police bicycle registration sticker and know that they stopped using that format in 19xx, or that bb sticker wasn't applied after a certain date, yadda yadda yadda, they don't tell us much except that it was most likely a Japan-market bike that spent some of its life in Japan.

I think the bb sticker is some kind of code certification sticker. The N.B.I. is probably "Nihon Bicycle Institute," or something similar, "Nihon" = "Japan," and you can also see the JIS logo, "Japanese Industrial Standards." It's a Japanese-market, probably older logo, written Japanese style, top>bottom, right>left. JIS certainly had build/dimension? codes for bicycles, and the sticker probably sez the NBI certifies the bike conforms to Code #6109, whatever the heck that is. It's hard to imagine the number could be a sequential thing, meaning the next bike off the line would have #6110, the #6111, etc. I reckon they all had the same #6109 sticker.

Japanese had/have? a love for bureaucracy, and JIS was/is? everywhere. Bike people can go nuts when they see a JIS stamp on a bike part, but I used to chuckle every time I changed a roll of toilet paper in Japan and saw the JIS logo molded into the plastic toilet paper holder spool. Makes sense, I guess---if the holder's too fat, the roll won't fit, and if it's too skinny, the roll will rattle around and maybe erratically dispense the paper. You try to tear off a discrete 3~4-sheet chunk, and 20 sheets rocket out. Chaos will ensue. It's a tough job, but somebody's gotta do it!