Unless this is a very recent development, I do not think Namiki uses serial numbers.
The number to which you infer must be the model number. For example, I have a Pilot (Namiki, overseas from Japan) Bamboo in front of me with the following number on the clip tag and box. There is no serial number on the pen.
FBB2MR-B-M20000
F = Fountain Pen
BB2MR = Model Code (there might be an internal definition of the letters and numbers)
B = Color
M = Nib Size
20000 = Price of the pen in Yen.
There is a lot of information available about Pilot/Namiki on the net and there are many knowledgable collectors and salespeople who can assist with questions. What information do you seek?
If you wish to see an online catalogue you can visit thier website:
http://www.pilot.co.jp/products/pen/index.htmlAn online dealers site is:
http://www.pen-house.net/pen/pilot/index.htmFor rudimentary translations of the above, cut and paste at babelfish.com.