I have two issues with the scheme that need clearing up. The first is vehicles on SORN of which others have commented - they should be included if you comply with the other requirements.
The second relates to vehicles that meet all the requirements concerning age but were not registered in with DVLA but perhaps imported from elsewhere. In my case I have a Toyota Starlett which was first registered in Ireland in 1997. I imported the vehicle into the UK in 2002 when I registered it.
So although I am interested in buying a new car and potentially have 2 cars that could qualify neither of them currently do!