For me one of the biggest ironies of this brilliant story that seems to capture the whole difficulty of presenting any established "truth" in the face of war and what happens during war is the way that O'Brien seems to offer us conflicting versions of the truth and then at the end withdraws those truths indicating that they are all in fact falsehoods:
All you can do is tell it one more time, patiently, adding and subtracting, making up a few things to get at the real truth. No Mitchell Sanders you tell her. No Lemon, no Rat Kiley. No trail junction. No baby buffalo. No vines or moss or white blossoms. Beginning to end, you tell her, it's all made up. Every goddamn detail--the mountains and the river and especially that poor dumb baby buffalo. None of it happened. None of it.
What is interesting about this story is the way that O'Brien seems to be reaching beyond a simple relationship between truth and falsehood and points towards the ambiguous nature of "truth." Even events that appear to contradict each other can actually both be true. In spite of the way that this story ends, the irony of this story is that although "none of it" happened, it still conveys one truth, as truth during war time is shown to have many different forms and appearances. The truth of what actually happens and the truth of what seems to happen is perfectly demonstrated by the death of Curt Lemon, who was actually killed by a rigged 105mm round, but to O'Brien's mind is killed by sunlight. We as readers who have not experienced war expect a simple dichotomy between what is true and what isn't. The central irony of this story is that we never know for sure what did happen and what didn't happen, and what just "seemed" to happen from O'Brien's perspective. O'Brien denies us the simple sureties of our lives by presenting us with a "true" war story.