I had a colleague once who couldn't handle vagueness. Whenever he talked about things where specific details weren't present, he would just make up those details. The thing about it, though, was that he didn't do it deliberately, but he unconsciously filled in the gaps and honestly believed that the details were there the whole time. And then, over time, as his memories of those details faded, he would make up new details to fill in the new gaps. This is what I think Jay is doing. The declarations (Adnan killed Hae) and major details (Adnan strangled her, Adnan lent Jay his car, they were at Leakin Park at some time) stay intact, but the minor details (where did Adnan show him the body, what time did they go to Kathy's, etc.) shift around because they keep getting overwritten.