ἐστράφθην is Ionic and Doric; Hom. and Hdt. have ἐτράφθην from τρέπω. Hom. has ἐτάρφθην and ἐτέρφθην from τέρπω
c. Primitive verbs showing in their stems the gradations ε (ει, ευ): ο (οι, ου): α (ι, υ) have a strong form, as ἐτρέφθην from τρέπω (τρεπ-, τροπ-, τραπ-)
d. Primitive verbs showing in their stems a variation between ε: η and ο: ω have, in the first aorist passive, the short vowel. Thus, τίθημι (θε-, θη-) ἐτέθην, δίδωμι (δο-, δω-) ἐδόθην.
e. Final ν is dropped in some verbs: κέ-κρι-μαι, ἐκρίθην. See cross491.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].