ἄν may be omitted in the apodosis of an unreal condition when the apodosis consists of an imperfect indicative denoting unfulfilled obligation, possibility, or propriety. Such are the impersonal expressions ἔδει, χρῆν, ἐξῆν, εἰκὸς ἦν, καλὸν ἦν, etc., with the infinitive, the action of which is (usually) not realized.
εἰ ταῦτα ἐποίει, ἔδει (ἐξῆν) αἰτιᾶσθαι αὐτόν
εἰ ταῦτα ἐποίησε, ἔδει (ἐξῆν) αἰτιά_σασθαι (or αἰτιᾶσθαι) αὐτόν
a. Here ἔδει and ἐξῆν are auxiliaries and the emphasis falls on the infinitive. The impersonal verb has the effect of a modifying adverb denoting obligation, possibility, or propriety: thus ἔδει αἰτιᾶσθαι αὐτόν is virtually equivalent to δικαίως ἂν ᾐτιᾶτο, and εἰκὸς ἦν αἰτιά_σασθαι αὐτόν to εἰκότως ἂν ᾐτιά_θη
b. ἔδει, χρῆν, etc., may be used in simple sentences ( cross1774 ff.) without any protasis either expressed or implied. But a protasis may often be supplied in thought.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].