In the U.S. there is no central registrar, deeds are recorded at local level, and owners are regularly found by collecting property tax. Back tax is tracked independently of ownership so if true owner fails to pay tax within a few years there is lien or foreclosure.
I'm guessing in Slovakia they might only tax sales or income of property rather than passive enclosure? If back taxes are levied on parcel the owners should immediately make themselves known.
"The Earth belongs in usufruct to the living. The dead have neither powers nor rights over it" - Thomas Jefferson