It is possible to have a vehicle that was first registered before 31st March 2001 that qualifies for CO2 related road tax. 31st March 2001 was the date when it was compulsory for emissions data to be included on the vehicle's CoC. Any vehicle imported after this date and before 31st March 2012 would qualify for CO2 related VED. After 31st March 2012, only vehicles first registed (anywhere) after 31st March 2001 qualify for CO2 related VED.
Our 1999 Lupo 3L (imported 2004) might be the oldest car that qualifies for CO2 related VED and also the oldest car that is compliant with the T-charge. Had I registered the other Lupo a month earlier, we would have one 1999 Lupo that qualifies for CO2 related VED and a 2001 Lupo that doesn't!
RAB