This is not an anomaly, and it does not date to 2016.
Legislative provision requiring production of a driving licence in court for certain road traffic offences was introduced in 2002. This was done because the Road Traffic Act 2002 introduced penalty points for the first time, and that Act therefore required production of a driving licence in cases which could involve the incurring of penalty points. The focus on cases relating to penalty points was to ensure recording of licence details if the person was convicted, and was there from 2002.
The 2016 amendment revised the procedure for production of a licence under the 2002 Act, as the existing procedure was felt to be less than optimal.
Where a person receives a disqualification from driving from a Court, they are legally required to return their driving licence to the Road Safety Authority. While it is true that this requirement is not met in many cases, the crucial issue in terms of public safety is whether people drive while disqualified. A person might return their licence and continue to drive, or not return their licence but not drive. Return of licences, while desirable, is no guarantee that a person will not drive after disqualification, and the figures not returning licences are not a proxy for the numbers driving while disqualified.