The geared versus DD issue is probably why Matt tested the motors and props for his P38 in a wind tunnel, to get more realistic measures.
Yeah - certainly the static numbers don't tell the whole story. On paper a N-20 DD w/GWS 3x2 looks the same as a KP-00 w/85x45mm, but on an actual airplane, the KP-00 wins out every time (at least in my experience).
bmutlugil - I had suspected the numbers were a date code, and that pretty much confirms it.
BTW-I measre 1.8 ohms on the N-20 LV and 3.6 ohms on the motor from the GWS LPS-B2C gearbox. The GWS motor definitely looks different in a number of ways, so I think Gordon is right that it's not from Mabuchi.
Interestingly, at the Mabuchi Web Site
if you search for "FF-N20" there is a "N20PA" rated at 3V and "N20PN" rated at 5V - so perhaps we should start calling the FF-N20PN (the common surplus motor) the "N20 MV" for "medium voltage"
As far as the cost difference goes - I'd guess that for some reason the factory produced a billion of these things, only to not find buyers (perhaps a buyer reneged), so they dumped them on the surplus market. And clearly enough were dumped to last a long, long time...