Comment by jdietrich
Per their own data, the DVLA are responsible for the records of 52 million drivers and 46 million vehicles. Those records are immensely complex, because they reflect decades of accumulated legislation, regulation and practice. Every edge case has an edge case.
There's someone, somewhere in the bowels of the DVLA who understands the rules for drivers with visual field defects who use a bioptic device. There's someone who knows which date code applies to a vehicle that has been built with a brand new kit chassis but an old engine and drive train. There's someone who understands the special rates of tax that apply to goods vehicles that are solely used by showmen, or are based on certain offshore islands. God help any outsider who has to condense all of that institutional knowledge into a working piece of software.
Government does not have a good track record of ground-up refactors of complex IT systems. The British government in particular does not have a good track record. Considering all that, the fact that most interactions with DVLA can be done entirely online is borderline miraculous.
https://assets.publishing.service.gov.uk/media/675ad406fd753...
I would be really really surprised if the database actually encodes all of these edge cases you are thinking about in a structured way. In other words, I really doubt there's code like `if engine_age > drivetrain_age` or whatever.