The French EU Customs brochure (mirror) states:
Les bagages personnels sont ceux que le voyageur présente au service des douanes lors de son arrivée. Il s’agit aussi des bagages que le voyageur présente ultérieurement à ce service, sous réserve qu’il justifie qu’ils ont été enregistrés comme bagages, au moment du départ, par la compagnie qui a assuré son transport.
Personal luggage is that which the traveler presents to the customs service upon arrival. This also applies to baggage that the traveler subsequently presents to this service, provided that they prove that it was checked in as baggage, at the time of departure, by the company that provided their transport.
What is non-personal luggage in the eyes of EU customs? I thought passengers would present all their luggage to customs, and that subsequently all luggage would be regarded as personal luggage in the eyes of EU customs