I don’t think I saw the form τάρπησαν before, or maybe I did, but simply forgot. Anyway, it made me check the verb τέρπω and I found the quite bewildering number of forms this verb can take in the aorist, both medium or passive:
Better still, they seem to have all the same meaning. Even by Homer’s standards that 's quite a baroque proliferation of forms. Or is there a distinction in meaning between the passive and medium forms?
The proliferation of forms of this and other verbs in the Homeric poems is a result of the oral character of the tradition that gave rise to them. The oral tradition that swept up words and forms from different phases of the language and different dialects, reflecting the evolution of the tradition. These words and forms were embedded in formulaic expressions which could only be updated to the contemporary language of whoever composed the poems if the more modern forms happened to fit the meter; otherwise, the older words and forms were preserved.
And the availability of alternative forms for the same morphological categories would have been useful to an aoidos composing orally, in performance, giving him (or her?) several metrically distinct choices that could be inserted in different metrical slots.
The list is misleading and unusable as it stands. You need to note the actual forms used, including the unaugmented ones, and their metrical context. Then it becomes interesting, very. (All the more so if ετραπην is not from τρεπω.)
The list that Bart gave. LSJ counts 5 aor med/pass forms, not counting augment/reduplicatn variatn, and indicates some distinctns of use under its various headings.
Basically you have both strong and weak forms in both passive and middle, plus some τερ-/ταρ-/τρα- interchange. Some locutions formulaic, some arguably ad hoc; several Od only. Esp interesting: metrically identical variation (not much), and confusion with forms of τρεπω (very little).