Cartridge without serial?

It's not the consumers fault - consumers will buy at lowest price if all things equal.  Sounds like the mfr isn't willing to do much at the top end and wants to blame the consumer.  I think the mfr's should own up to their product and provide support regardless where it was bought.  There are some companies that do that. Recently, I was talking to Tri of Tri-Planar who said that he supports his products regardless of where it was bought. Now that's ethical.

@chakster  You explanation would apply for a very large conglomerate that sells very high volume.  I highly doubt that any of the cartridge manufacturer's are in that league. Surely they must know all of their distributor's and exactly what product they are shipping to them. I would be surprised if Nakatsuka-San is making and selling a hundred pieces a year-- in total! 
Therefore, it seems odd to me that this situation is going on, unless of course something else is occurring ( which I suspect strongly that it is!).

cartridge without a serial number would make me wonder if its real, knockoff/or stolen.   

@daveyf even if you know your distributors how you can catch one who sold to grey market dealers a bunch of them (if serial numbers replaced with fake number)? This is the only reason to remove or to replace serials, this is ID of the source. 

Okay nowadays it is possible to fake everything, but faking entire cartridges could be pure fantasy.
It could be stolen material and consequently the serial number label is removed if it is not engraved on the same body cartridge.