Either BMW changed their mind or overstated what they’re doing, because they are on-record contradicting this story: https://www.motoringresearch.com/car-news/bmw-targeted-warra... BMW has told Motoring Research its targeted billboard warranty adverts – which are claimed to use number plate registration technology to tailor public adverts to BMW drivers – do not actually draw upon vehicle warranty status. Rather, onl…
That sounds like a weasel word version of "we can detect vehicle warranty status without using PII."
Using that info it would be trivial to detect a BMW car that was older than X years old. Where X is number of years the normal non-extended warranty is. You then just assume that any car older than the non-extended warranty doesn't have an extended warranty and display the advert.
Then the only thing the advert would be giving away is that there is a BMW nearby that older than X years. Which anyone with a pair of eyes could figure out because the numbers of UK numberplates encode the issue year (thus the age of the car), and well, BMW's are pretty easy to identify just by looking at them.