Just wanted to post to note an alternative serial number scheme for Kuwahara that is used for their BMX bikes, but what surprised me is that it seems to be what was used on my 1983 road tandem:

QyMxxxx; where Q is the place of manufacture: T=Tange, K=Kuwahara, KG=Koizumi, G=Giant, etc.

More details at kuwahara(dash)bmx(dot)com

Thanks for providing this resource, I have found it useful to confirm information on more than a dozen bikes.

-Will