Contradictions and Authentication in Aphra Behn's 'Oroonoko' (PDF)

I was my self an Eye-Witness to a great part, of what you will find here set down; and what I cou'd not be Witness of, I receiv'd from nthe Mouth of the chief Actor in this History, the Hero himself, who gave us the whole Transactions of his Youth; and though I shall omit for Brevity's sake, a thousand little Accidents of his Life, which, however pleasant to us, where History was scarce, and Adventures very rare; yet might prove tedious and heavy to my Reader, in a World where he finds Diversions for every Minute, new and strange (...).

With this truth claim opens the Story of Oroonoko: Or, The royal Slave. A True History and for the reader it is apparently a sound starting point that the soon to be encountered story is in fact no fiction but a true history. Aphra Behn was perhaps the first author who employed this technique at that time. Similar claims can be found in Richardson's Pamela and in Robinson Crusoe and yet they still had been published almost half a century later.
Oroonoko is the story of an African prince who was captured and enslaved. In the first part of the book that takes place in Africa, he is in love with Imoinda, one of the king's mistresses. After their affair is given away, Imoinda is sold into slavery. Soon afterwards, Oroonoko is lead into an ambush and taken to the English colony of Surinam where he meets coincidentally his beloved Imoinda again. She gets pregnant and he offers his masters a ransom so that their child can be born in freedom. After many empty promises of his master Trefry, Oroonoko leads the slaves into a rebellion. He is captured one more time and decides to put his and his wife's life to an end. Will he have the guts to do it?