As I noted in a previous post,
biblical historiography’s treatment of the sixth cent. bce destruction of Jerusalem is discussed at great length in “The Destruction of Jerusalem
and Biblical Historiography,” by Oded Lipschits, The Fall and Rise of Jerusalem. Judah under Babylonian Rule (Winona Lake:
Eisenbrauns, 2005) 272-359. I think Lipschits is right to conclude that Jer
39:3 is part of a larger composition ("the biography of Jeremiah")
the completion of which is to be dated to 586-560 bce (350), and that the addition of 39:4-12 thereto belongs to a
somewhat later period, between 560-538 bce.
Against Lipshits, but in agreement with the evidence of LXX Jeremiah, which preserves, according to a widely-held hypothesis I find convincing, a “first” edition of the book of Jeremiah, I believe 39:13 was added to a pre-existing base at the same time as 39:4-12: all of 39:4-13 is missing in LXX Jeremiah. Lipschits dates the composition of 39:13 to the same period as 39:3.
If MT Jeremiah reflects a rewrite of an earlier edition of a book reflected in LXX Jeremiah, a number of apparent contradictions in MT Jeremiah 39:1-40:1 find a satisfactory explanation. Based on the reconstructed Vorlage of LXX Jeremiah 46 (=MT Jeremiah 39:1-3, 14), the narrative in the first edition sounded like this:
In the ninth year of Zidqiyáhu king of Yehúda, in the tenth month, Nabû-kudurri-úṣur king of Babíla and his whole army attacked Urušalēm and laid siege to it.
In the eleventh year of Zidqiyáhu, on the ninth day of the fourth month, the city was breached, and all of the officers of the king of Babíla made their entry, and occupied the middle gate – Nergal-šarri-úṣur potentate of Simmagir, Nabu-šarrussu-ukin the Rab-ša-rēši, Nergal-šarri-úṣur the Rab-mugi, and the remainder of the officers of the king of Babíla. And they had Yirmeyáhu taken from the guardhouse’s courtyard, and they entrusted him to Gedalyáhu ben-Ahikam ben-Shaphan. And he led him away and he dwelt among the people.
According to this narrative, the release of Yirmeyáhu to the protection of Gedalyáhu was among the Babylonian officials’ first acts upon entering the city. This seems to clash with a second account, LXX Jeremiah 47:1 (=MT Jeremiah 40:1), in which we read:
Nabû-zēr-iddina the Rab-ṭabah̬im released him [Yirmeyáhu] at Ramah where he had taken him in fetters in the midst of the Yehudean deportation, those being deported to Babíla.
A third account is found in MT Jeremiah 39:11-14, which reads:
And Nabû-kudurri-úṣur king of Babíla gave orders through Nabû-zēr-iddina the Rab-ṭabah̬im concerning Yirmeyáhu as follows: “Fetch him and keep your eyes on him, and do him no harm; rather, do exactly as he asks of you.” And Nabû-zēr-iddina the Rab-ṭabah̬im had, along with Nabû-shēzibanni the Rab-ša-rēši and Nergal-šarri-úṣur the Rab-mugi and all the Rabs of the king of Babíla – and they had Yirmeyáhu taken from the guardhouse’s courtyard, and they entrusted him to Gedalyáhu ben-Ahikam ben-Shaphan that he might take him away, into the [=Gedalyáhu’s?] house. And he dwelt among the people.
In my view, the three accounts are compatible if one assumes that MT Jeremiah 39:1-14 represents a rewrite of LXX Jeremiah 46:1-3, 14 in which the actions of Nabû-kudurri-úṣur’s top official, Nabû-zēr-iddina the Rab-ṭabah̬im, are brought to the fore. On this hypothesis, Yirmeyáhu was released to the protective custody of Gedalyáhu by Nergal-šarri-uṣur potentate of Sinmagir and company when the city was breached. Later, in accordance with the express command of Nabû-kudurri-úṣur carried to the scene by Nabû-zēr-iddina the Rab-ṭabah̬im, Nabû-zēr-iddina and company had Jeremiah brought to Ramah along with those to be deported to Babíla. At that time they re-released him to the protective custody of Gedalyáhu. Nabû-zēr-iddina had appointed Gedalyáhu over the cities of Yehúda in the meantime (40:5).
The chief argument in favor of the above reconstruction is that it accounts for all of the textual data in hand, that found in LXX and that found in MT Jeremiah, without once pulling a idiot redactor or careless scribe out of a hat as an explanation of the textual situation.
offered by others assume gross error at one or more stages in the textual
process. Lundbom presumes that LXX Jeremiah is the artifact of a dimwitted
scribe who inadvertently skipped over words, phrases, and whole paragraphs at
various points throughout the book. The hypothesis boggles the
imagination. The more common assumption that both LXX and MT Jeremiah attest to a
plethora of textual dislocations, corruptions, and conflations also strains
credulity. It stands to reason that the Vorlage of LXX Jeremiah insofar as we
can reconstruct it, and MT Jeremiah, reflect an accumulation of instances of
error in the course of textual transmission, but the amount of error MT and the
parent text of LXX are presumed to contain by Holladay, for example, needs to
be treated with caution.
A funny thing happens to people in the study of ancient texts written in a language and against a historical background of which our knowledge is partial at best. At first blush, a number of details seem amiss. The temptation is strong to adjust them in accordance with what we think we know.
But the more one comes to understand the ins and outs of the ancient language, and the better one's grasp of the historical and theological context, the less often details seem amiss.
Whenever a text seems to be in disarray - it matters not at all whether the text is found in the Bible or outside of it - the better assumption is that our understanding of the text is in disarray. Call this, if you wish, the first rule of hermeneutics. The second is like it: if the text still seems to be in disarray, it is still the better assumption that our understanding of it is in disarray.
 Jack R. Lundbom, Jeremiah 37-52: A New Translation with Introduction and Commentary (AB 21C: Garden City: Doubleday, 2004) 81, and passim in his three volume commentary.
 William L. Holladay, Jeremiah 2: A Commentary on the Book of the Prophet Jeremiah Chapters 26-52 (Hermeneia; Minneapolis: Fortress, 1989) 268-69; 291-93, and passim in his two volume commentary.