What should I do if I find a passport I'd previously reported lost/stolen?

Never travel on your passport if it has been reported lost or stolen. You run the risk of being stopped at border crossings, as Interpol keeps a record of all reports of lost or stolen passports.

If living in The Netherlands you should return the passport to:

Passport Officer,
Embassy of Ireland,
Scheveningseweg 112,
2584 AE,
The Hague