Registered is when DVLA first registered the vehicle — the
date the MOT record itself is keyed on. It takes 2018,
2018-06 or 2018-06-30, and a part date means the
whole of the period it names. The year of manufacture is shown on each result
but is not a filter: it is derived rather than recorded, and for an import it
can be years off the registration date.
Mileage is the odometer at the last MOT, so it is only as
recent as that test — a vehicle off the road for years still reads whatever it
read when it last passed. Readings recorded in kilometres are converted, so
the range means miles whichever unit the tester entered. Either end can be
left empty for an open-ended range.
Country reads the three-digit mission code on a diplomatic
plate — the embassy, high commission or international organisation the vehicle
belongs to. Pick more than one to compare them. A mission can hold several
codes (France is 152–156), which are searched together, and some codes name a
convention rather than a country: 350–399 is an undisclosed mission, 600–649
visiting royalty.
Issued in is the DVLA region that first issued the plate —
roughly where it was first sold. It is not where the vehicle is now, and says
nothing about its keeper. Local offices closed in 2013, so it is weaker on
newer plates. Pick more than one to compare regions, as with
age ident. and paint. Personalised and dateless
plates carry no region or age at all, so pairing one of those under
plate style with issued in or
age ident. creates an impossible search
— the search will not run, and will say which two filters to choose between.