The Verdict: Not eligible
There is no route to restore nationality taken under article 19. The routes left are ordinary naturalisation for someone living in Greece, which our Naturalization quiz covers, and a statelessness determination.
Article 19 of the 1955 Code let the state declare that a person of non-Greek ethnic origin who left Greece without intending to return had lost Greek nationality, without consent or notice. About 60,000 people lost it between 1955 and 1998, mostly from the Turkish minority of Western Thrace. Many were left stateless.
Law 2623/1998 repealed it on 11 June 1998, but not retroactively, and no restoration was enacted. Greece promised to naturalise stateless people still living in Greece, but that was policy handled case by case, not a right.
Individual histories vary and this population has been the subject of long litigation, so specialist advice on the individual case is worth having.