That would be a 512k upgraded to a Plus. The Plus rear bucket had an indent on the bottom for the serial. The missing placard is because the upgrade never installed on. The upgrade kit came with at least two placards to cover 110v/220v and other country origin info. For the US that would be FCC stuff. But the FCC has no place in other countries. There was an upgrade kit sold on eBay not to long ago that showed all of this, but the motherboard was missing from the kit.