I really didn't understand much of that

We have a simple system here, at least. Each DMV station has it's set of letters, and the numbers are consecutive. Normally, the plates follow the car for it's entire lifetime, but a new registration number is normal if your plates have been stolen.

Example: Oslo started with DA back when the plates were introduced, not they are at DL. So, the first car registered in Oslo with these plates, which were introduced in 1971, was DA 10000. Following DA 99999 was DB 10000 and so on.

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If you have a 5 cylinder, you don't need a stereo.

1999 Audi A6 quattro
1990 Volkswagen Golf CL Syncro
1987 Audi Coupe quattro