The Verdict: Need More Info
Find out who left Greece, when, and whether anything was recorded taking away their nationality. A municipal or community register, a consular record or their papers abroad will usually show it.
Only one group has a dedicated law. Article 13 of Law 4018/2011 restores nationality to a living person of Jewish origin born in Greece up to 9 May 1945 who was Greek from birth, and gives their direct descendants a naturalisation right.
People stripped under article 19 of the 1955 Code between 1955 and 1998, about 60,000, have no restoration route. Neither do families displaced by the occupation or the civil war.
If nothing was ever recorded taking nationality away, the family may still be Greek, and our Citizenship by Descent quiz is the place to start. Otherwise take this quiz again once you know which group fits.