How can a "registered car" is called "unregistered" linguistically. Once registration is entered, it can not be extinct, can it?

Question

"Once your registration expires, your vehicle becomes unregistered."

When I read the sentence, the word "unregistered" got me thinking, because "unregistered" means "not registered", in other words "never written on a paper or on any medium" In the case of cars, I would understand that an unregistered car would be a car which has just came out of manufacturing process, and has not been bought by anyone yet. And it will be registered when somebody buys it.

Or it may be that your move to another state, and in that case your car is unregistered in that new state, because it was never registered there. So it makes sense.

However, when it comes to a car which has already been registered in a book or other medium, the word "unregistered" sounds weird. We know that they were actually registered some time in the past, and -as part of that registration- they were appointed or given a time period. It is only that this time period has expired, but the registration is still there.

So, the registration has not disappeared or has not become extinct. In fact registration is still on the same paper (or whatever medium it was written on) with only a warning that time period appointed has expired.

To sum up, it is not the registrations that expire, but it is the time period that expires, and this time period is not the whole registration. It is only one of the many fields that comprise the registration which consists of many fields (name, date of production, brand etc). Even if that period has expired, the registration about that car is still there and the book or the database will continue to have a registration about that specific car. Just like a student who graduates from a school does not become "unregistered". His registration at the school will always stay there. An unregistered student would be one who has never started at that specific school.

Considering all these logic, why call these cars "unregistered cars" instead of something like "cars whose appointed time has expired"?

Answer 1

You are wrong that "un-X" means "never having been X" There is no such logic.

It is quite natural to express the idea that "a car whose period of registration has ended" as "unregistered car".

An "undressed person" is not a person who has never worn clothes. It is a person who has removed their clothes. There are many other examples which show that "un-" means "not currently" and doesn't mean "never".

Answer 2

Unregistered does not mean "never written on paper, or any medium". You could maybe use unwritten for that.

From Cambridge dictionary online:

register: to put information, especially your name, into an official list or record

When you register your car, it gets put on the official list of vehicles that can be driven on public roads. When your registration expires, your car gets deregistered - taken off the official list. It is now unregistered - not on the official list.

It's useful to have a single word to describe this state, rather than an elaborate phrase.

Second point: when a website gives you a sentence like that, especially a government website, they are telling you what that word means in their writing. Even if you didn't know what the word meant, or thought it meant something else, now you know what it means. That's why they put that sentence there.