The italic emphasis on "been" implies a disassociation with of the PB550c and Japan. And seeing that you live in the UK seems to imply that you are not alone in owning a PB550c there? Was the PB550c indeed sold widely in Europe?
Everything I have studied about the PB550c suggests it was built by Apple for the Japanese market, and sold exclusively in that market. I also lived in Japan during the release of the PB550c and can remember articles in Japanese about that fact. Nevertheless, if there is strong evidence to show that the PB550c was also sold directly by Apple to other markets (such as Europe), that would be news of interest to the classic Mac community. Please educate us, Neil!
dogcow, your fine hi-rez photo (bless you!) shows that you have Mac Plus ROMs in your logic board (342-0341 & 342-0342). In other words, it's a 512ke.