In Syme's The Roman Revolution, he suggests that it was likely Octavianus who was quietly behind the first edition of Cicero's collected correspondence. Later, he mentions that letters between Cicero and Octavianus were conveniently elided from the edition. Is that the main evidence for believing Octavianus was behind the edition of Cicero's correspondence? What does contemporary scholarship tell us about how Cicero's letters come down to us?
I wasn't able to find the relevant passage in Syme, and Octavian isn't a potential editor or publisher in the scholarship on the letters I am familiar with (though he is a possible censor of the letters). Could you point me to the passage? Anyway...
We know next to nothing of the circumstances of the publication of Cicero's corpus.
We have four extant collections of Cicero's letters: the Letters to his Friends, the Letters to Atticus, Letters to Brutus, and Letters to Quintus. Most scholarship addresses the first two collections, and I'm going to follow that tradition.
Here's what we know about about publication:
Cicero appears to have planned to publish some of his letters, and wrote to Atticus saying Tiro was making a collection of about 70 letters and needed to get some letters from Atticus himself.
The first reference to a collection is in Nepos (d. ~25 BCE), who had to go to Atticus' house to use it - it was in fact a private collection still, and not in circulation.
The earliest quotations appear to be in Seneca (d. 39 CE), who used phrases found in Letters to his Friends, and Beard among others takes this as evidence that by the 30s CE that collection was in circulation.
The younger Seneca (d. 65 CE) used quotations from the Letters to Atticus.
Those are the three data points that most scholars accept. In the 30s BCE they hadn't been published, but by 30ish CE Friends seems to be circulating, and Atticus by the 60s CE.
Some people, starting from Buecheler (1879) and perhaps most influentially Shackleton Bailey propose a "late" date for especially the Atticus based on a couple of points. The quotations in the two Senecae might not be evidence of collections circulating but rather individual books or even letters. The earliest citation to a specific numbered book of a collection occurs in Aulus Gellius, a 2nd century CE writer. Asconius, a mid-1st century CE author who wrote commentaries on Cicero's speeches didn't seem to know of the existence of the letters, but used other unusual sources like the acta. However this argument, particularly relying on the argument ex silentio Stewart (1962) destroyed (before Shackleton Bailey published). In her 2010 essay on Cicero's letters, Mary Beard doesn't even consider this a possibility.
There is also an early date proposed by Carcopino in 1947, who wanted to put the publication to before the battle of Actium in 31 BCE, and the editors were Tiro, Atticus, and Cicero's son. Mary Beard only admits this possibility because she can't dismiss the possibility that individual letters edited by Tiro went into circulation early, and were only collected later.
With those potential publication dates, we have limited choices. If we believe an early publication, we have three possible names: Atticus, Tiro, and the younger Cicero. We know Tiro had a collection of 70 letters Cicero intended to publish (somehow) and that Tiro's collection wasn't complete. We know Nepos saw a collection of Cicero's letters at Atticus' house - clearly unpublished. If the collections were edited or collected after about 30 BCE, we don't have any candidates for named editors.
If we suppose the collections appeared sometime between 30 BCE and 30-60 CE, we might suppose Octavian was involved in suppressing the letters, but we're clearly into guesswork territory here.
I used Setaioli's 1976 review of the scholarship in Symbolae Osloenses 51:1, and Mary Beard's article in Wiseman, Classics in Progress, 2010, to remind myself of some names and dates, but I've been looking at a lot of stuff about these letters for a little bit now.