There can really be very little doubt on the matter.
What we may doubt, however, is not the authenticity, but the value of the History as an historical document.

Without question, Swift wrote in good faith; but he also wrote as a partisan, and a partisan with an affectionate leaning for the principal character in the drama he was describing.

Orrery was right when he called it "a pamphlet," and "the best defence of Lord Oxford's administration." As a pamphlet and as a defence it has some claim on our attention.

As a contribution to the history of the treaty of Utrecht it is of little account.

Swift could not, had he even known everything, write the true story of the negotiations for publication at the time.