Except for a, all initial unaccented vowels dropped at one stage in the history of Greek. But irregularities appear as vowels were reintroduced from learned influence or by analogy. Many dialects of Modern Greek retain an unaccented epsilon past indicative augment. Crasis across clitic boundaries played a role.
Thumb’s Handbook of Modern Greek includes discusses this in the vocabulary section 182.
In Palasa imperfect second person plural επίνετε is heard much like ancient greek imperfect, by contrast with the SMG πἰνατε imperfect.