I have read his books and I suspect he deliberately changed some details for literary purposes. Of course Holocaust deniers might question much of what he wrote but do serious historians also cast doubt on some important details of his Survival in Auschwitz and The Truce (The Reawakening). A question I have is simply why the guards left anyone alive to bear witness. I know that the guards were in a hurry; I also know that they had actually been instructed not to kill remaining Jews by Himmler to use as bargaining chips (of course murders continued sometimes anyway) and perhaps Levi's survival has something to do with Himmler's directive.
EDIT: I would say, what important aspects of Levi's books are either considered heavily fictionalized or outright falsehoods? I know that various characters, even though given pseudonyms in the books, were real people but from memory, I question things like the above-mentioned fact that he was left alive, what circumstances allowed this since nazis were still in killing mode long after the war was clearly lost. There is a scene where an Allied prisoner of war gives Levi a thumbs up: POWs really interacted (at a distance even) with Jewish inmates?