When they say “ Information captured at the Roadside Automatic Number Plate Recognition system. Only vehicles matching specified criteria (e.g. expired test) are captured.” - meaning, that’s what in the dataset. But they have to read every plate to check its expiration status etc. they just don’t put it in this dataset.
But also … how is ANPR in Europe PII? Is there a public/semi-public database that connects plates to owners?