ALTHOUGH he was on missing childlists in the United States for 12 years,U.S. citizen Mark Saunders was neverreally lost. He had been living in CostaRica until he turned 18 in July andreturned to the United States for the firsttime since he came here at age 6, caught ina custody battle that crossed internationalborders.Saunders considers that he won thatbattle, and before leaving Costa Rica earlierthis year, he wrote an open letter thankingthe country for its help in that victory.Saunders was brought here in 1993 byhis maternal grandparents, who had raisedhim since he was 1.Months before their arrival,Saunders’ father was granted custody ofhis son. Despite the father’s efforts –through U.S. courts and extraditionrequests – Costa Rican officials determinedSaunders was best off with hisgrandparents in Costa Rica.