Trumble for what it's worth, I too purchased the Denon 103r from New Audio United as a temporary replacement while my Dynavector 20x2L is getting repaired by Soundsmith.
I called the company and they assured me that the cartridge is real and they get their cartridges from dealers in Japan, because they are not an authorized dealer. Obviously they can say anything they want until proven otherwise but I insisted they email me a reason why the top of the cartridge doesn't have a serial number sticker on it.
Even so, I have played about eight albums thus far using the cartridge, and if this is a so-called "fake" cartridge then it's a DARN GOOD fake, because the sound coming from the cartridge is really good so far and I haven't even come close to breaking it in, and I have listened to many Denon 103's and 103r's over the years.
I will however, keep you informed if I hear anything else on this matter, but so far so good.