In collector cars the word original does a great deal of work, and buyers who pay attention to it tend to do better than buyers who pay attention to paint.

What the file contains

Matching numbers means the engine, gearbox and body carry the identities they left the factory with. Around that sits the rest of the file: the build sheet or factory certificate, the ownership chain, period photographs, competition history where it applies, and invoices for every significant piece of work since. A car with a thin file is a car whose history has to be taken on trust.

What it means for an allocator

Restoration spends money. Documentation preserves it. A high quality restoration rarely returns its cost on sale, because the next buyer values originality over freshness and can see exactly what was replaced. The file costs nothing to keep and is the single thing most likely to decide whether a car sells into the strongest bid or the weakest. Keep the paperwork with the car, and when buying, read it before the drive rather than after.