The Verdict: Need More Info
Work out whether each link from your Greek ancestor to you runs through a father or a mother, and the birth date of each child. That shape decides almost everything.
Until 8 May 1984 only a father passed on Greek nationality. A line of fathers works however long it is, with no generation limit and no deadline. A Greek mother whose child was born before 8 May 1984 is where a claim usually stops, or turns into a weaker route.
For each generation, note the Greek-descended parent, whether they were the mother or the father, and their child's date of birth. Birth certificates or older relatives will usually give you this quickly.
Two things not to worry about meanwhile. Naturalising abroad did not end anyone's Greek nationality. And there is no deadline, so nothing is lost while you check. Then take the quiz again.