Present of Past and Present Combined.—The present, when accompanied by a definite or indefinite expression of past time, is used to express an action begun in the past and continued in the present. The ‘progressive perfect’ is often used in translation.
Thus, πάλαι θαυμάζω
a. So with
b. The perfect is used instead of the present when the action is completed in the present.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].