These could possibly be called "pre-production" vehicles, as they were likely built on the production line, but before the main launch of the Td5 model; they had VINs in sequence with the other Defenders being built. The first third were built between October 1997 and June 1998, presumably to tweak processes in production, and then from July 1998, more and more were built before the Td5 became the standard-spec Defender around 27th August 1998. Not only was there the change to the Td5 engine, but also the switch to the 1999 model year, which had a number of changes like completely new wiring looms.

Most of the "Unknown" vehicles are LHD, so would likely have been sold overseas. I have discovered at least one vehicle in Norway.