Current style number plates do not have that many letters.
LLNN LLL
First two letters may relate to the area of registration if not chosen as part of a personalised plate
Numbers relate to the year of registration of the car (the age, notionally). For numbers above 50, subtract 50 and know that it was the "mid way through that year" registration event. 21 = start of 2021, 71 = half way through 2021
Last 3 letters may just be a serially assigned rolling letter set if not chosen as part of a personalised plate
You're allowed to have a personalised plate make a car look older than it is, but not newer