For some reason, I don't know why, I've always assumed that an age related plate was issued from the "left overs" of that years numbers.
If numbers issued ran up to XYZ 850, then any issued afterwards started at XYZ 851 etc etc.
My son and I bought a car recently, an Eunos import, that was wrongly advertised and therefore potentially worth more than the asking price.
The thing is an MOT history check was showing things wrong from before it had been imported, and not only that, it was a Nissan and not a Mazda
After calls to the DVLA it turns out that the Nissan was written off then it's number allocated to our Mazda, previous history included.
Previous history now wiped so alls well.
Makes you think though. You do the searches, something shows up, you walk away.
Paul G