Originally Posted by
gq_dq
Really, this is indeed the first and pretty show-stopping mystery. Immigration would simply not have allowed OP to exit immigration and just walk on to the next flight. They would have held him+family in the secure Immigration area while the crew searched the plane... it would have been a pretty easy search.
If he is citizen of a schengen country he could have entered with his ID. Since his home location seems to BRU, I would place my bet on this.
Although it is expensive and takes up to 4 days, the second I would have realized my pp is lost, I would have tried to get a new express passport, even though I have a second pp.
My expectations towards any lost&found service is pretty low and that is the one thing that frightens me the most. Being stranded either abroad or at home because of lost papers.