I have been reading Literary Texts and the Greek Historian, by Christopher Pelling, President of the Hellenistic Society and Professor of Greek at Oxford. I was interested in how he resolved an apparent discrepancy between Thucydides' and Apollodorus' (as recorded by Demosthenes) accounts of whether a vote was required to bestow citizenship on Plataean refugees. It reminded me of one of my articles, "Harmonizing" The Gospels: Some Principles for Dealing with Purported Contradictions in the Gospels," where I quote R.T. France:
It should be clearly understood that a serious attempt to harmonize what purport to be historical accounts of the same event is not simply a perverse concern of Christian apologists. Any student of history, especially ancient history, is familiar with the problem, and any responsible historian confronted by apparently discrepant accounts in his sources will look first for a reasonable, realistic way of harmonizing them.
R.T. France, The Evidence for Jesus, page 112. France is a well-regarded scholar and it was interesting to run across an example of his reference to students of ancient history having to sometimes look for realistic harmonizations of apparently divergent accounts.
The context of Pelling's discussion is the fall of Plataea and the reported evacuation of a group of Plataeans to Athens. Plataea, one of the Greek City states involved in the Peloponnesian War, was besieged and then fell to the Thebans and their Spartan allies. In his speech on the subject, Apollodorus describes how a group of refugees from Plataea traveled to Athens and that the Athenians voted to make them citizens. Demosthenes 104-106. Thucydides, however, makes no mention of these refugees or a vote bestowing citizenship in his account of the fall of Plataea. Further, elsewhere in his account, Thucydides suggests that such a vote would be unnecessary because it had already been decided by the Athenians that Plataeans were joint citizens:
3.55.3 (Speech by Plateans: "We did no wrong if we didn't want to revolt from the Athenians... It would have been dishonorable to abandon them, especially since we ourselves had asked them to be our allies and had been treated well, enjoying joint citizenship.")
3.63.2 (Speech by Theban: "You yourselves say that you became Athenian allies and citizens in order to take your revenge on us.")
If Thucydides is right, then Plataeans already had Athenian citizenship and there would be no need for the vote recounted by Apollodorus. Moreover, Apollodorus is clearly indebted to Thucydides throughout, so perhaps he simply manufactured the account of the vote conferring citizenship out of wholeclothe. A Plataean Vote skeptic would seem to be within his rights to completely reject Apollodorus' account and go with Thucydides.
But classical historians are apparently not so skeptical. Or simplistic. In fact, according to Pelling, "[t]here is a growing scholarly consensus that both Apollodorus and Thucydides capture something of the truth." Literary Texts, pages 74-77. Thucydides, it turns out, had every reason to omit the vote granting citizenship and Apollodorus had every reason to include it. Nor even if we take Thucydides at face value about earlier grants of joint citizenship between Plataea and Athens should we conclude that Apollodorus is wrong on this count. It turns out that Thucydides is likely referring to an honorary citizenship or, at most, a citizenship that may be exercised on an individual basis, whereas Apollodorus is speaking on a grant of real citizenship to a large number of people who would have to be absorbed by a broader cross section of Athenian tribes.
If some form of honorary (or potential) citizenship had been granted earlier  such citizenship would have been available to any individuals who chose to come to Athens, but the arrival of a mass of citizens in 428/7 might necessitate a particular measure to distribute them around the demes and tribes. In that case, one can see why each other accentuated the elements he did. Apollodorus would naturally play down the earlier decree: his point is that the Plataeans' peculiar grant was only earned after quite unusual loyalty and sufferings. Thucydides would equally play down the final grant: his stress at the end is on Athenian non-involvement and passivity. One can also see why he includes the mentions of the earlier grant in the speeches. This may seem to fit the Plataeans' case, for it accentuates the bond with Athens and the moral claim which the Athenians had over them, thus extenuating their services to Athens; but the closer Plataea aligns herself with Sparta's and Thebes mortal enemy, the more certain her fate seems.
Pelling subjects the scholarly consensus to further examination before ultimately concluding that "we do better to remain with the scholarly consensus." He gives further reasons for concluding that Apollodorus had a reliable source in addition to Thucydides upon which he relied for the account of the vote to grant the Plataean refugees citizenship.
It is surely impossible to believe that [Apollodorus] has himself made up his decree: if he had, he would have made a better job of it, and there would not have been all those mismatches.... Isoacrates gives some support to the notion of a block-grant in 428/7 at Panathenacius (12) 93-4; and, more importantly, the wording of the decree itself tells against forgery. Osborne points out that both the omission of phratries and the assignation to demes and tribes are features of mass enfranchisements rather than the more normal individual grants, and a fabricator would be unlikely to know that. The decree's distinction between the present mass grand and the careful presentation of credentials for any subsequent grant is also suggestive. That points to a sudden arrival of a large number of individuals, and that suits 428/7.Id.
Pelling's case for the consensus harmonization of Thucydides and Apollodorus on this issue is persuasive. It shows that such harmonizations, although not to be undertaken without good reason, are part of the tools of the classical historian trade.