Rudolf Pfeiffer (Callimachus, ii.xxxvi–xxxvii) believed that, as a young man, Callimachus wrote four books of Aetia. To these the poet added in his old age a Reply to his Critics (fr. 1), and a slightly revised version of his recent occasional elegy, the Lock of Berenice (fr. 110, now including a nuptial rite which has survived only in the translation by Catullus, 66.79–88); this revised Coma became the last poem in Aetia book 4, to be followed by an Epilogue (fr. 112) which may mark a transition to the Iambi. Pfeiffer's theory generally held the field until the brilliant article of P. J. Parsons, in ZPE 25 (1977), 1–50. With the help of newly recovered papyrus fragments Parsons showed that a previously unplaced elegy celebrating a Nemean victory (fr. 383 Pf.) was connected to the story of Molorchus (frs. 54–9), who entertained Heracles before that hero killed the Nemean lion and instituted the Nemean Games; thus the poem belonged to Aetia book 3. Furthermore, various pieces of evidence converge (Parsons, pp. 46–8) to make it probable, if not wholly certain, that this substantial poem (some 200 lines long) stood first in its book. So it appears that, at least in the final form of the Aetia, books 3–4 were framed by two poems honouring the wife of Ptolemy III Euergetes, namely Victoria Berenices (Parsons' title) and Coma Berenices.

Soon afterwards a further important advance was made by E. Livrea (ZPE 34 [1979], 37ff.), who perceived, on grounds of subject-matter as well as papyrology, that the poor man who sets a mousetrap in fr. 177 Pf. must be none other than Molorchus; note particularly the probable mention of Cleonae in fr. 177.37 Pf. = Supplementum Hellenisticum 259.37. Thus a new fragment of 38 lines accrued to the poem.

These discoveries have some implications for the composition of the Aetia. Addition of a Coma Berenices (94 lines in Catullus' version) to a pre-existent Aetia book 4 could be countenanced easily enough, but, as Parsons says (p. 50), it would have required a much more radical, and therefore less plausible, revision for Callimachus to have added Victoria Berenices to a pre-existent Aetia book 3. Accordingly Parsons suggested that the original Aetia contained only books 1–2, united by the conversation with the Muses; then in his old age Callimachus compiled two more books, partly at least from poems already composed, and gave them a frame of two poems honouring Queen Berenice. Parsons' view has, I think, been widely accepted; Professor Lloyd-Jones wrote in SIFC 77 (1984), 56 ‘No-one has yet argued against the simple modification of Pfeiffer's theory of the two editions of the Aetia which Mr. Parsons based on this discovery. The first edition comprised two books only.’