ZGW
I know that you can choose every number which fits the system and it is not currently in use. I've heard you must pay for it.
That is correct. The extra fee for a chosen combination amounts to 10,20€.
Нец
Yes, of course, but I mean — which combination will you have if you don't want to choose?
From my expirience you will just get a random combination from a certain letter group that varies between districs.
A few examples from districs near me:
The UH district issued plates with the format "
UH-* 111".
The EIC distric issued plates with the format "
EIC-Q* 111".
The EA district issued plates with the format "
EA-* 111" but switched briefly to the format "
EA-* 1111" which was newly introduced by that time.
The numbers and letters on these plates would always be completely random.
Other districs may have different internal regulations for this and there might even be differences between two offices in the same district.
It should be noted that this is just my personal observation from the last five years and might not be necessarily 100% correct.