The Koumantaros family must have been a well off family in medieval times. Only 10% of all Greeks had a surname 500 years ago. The earliest records I have go back to 1500, Monenvasia, Peloponnese. Also, very recently two marriages indicate the same thing.
Koumandaros Katerina married Demitrios Negroponte 1938 ( A very rich (allegedly) Greek from Chios) and earlier, Eugenia Koumantaros married Spyro Niarchos in 1908 (well of person????)