Well, if they find her guilty the part you mention might be the one thing that they accept from the OS. Casey would have had to see and hold Caylee's dead body to triple bag her and to throw her in the woods.
I don't know... I can only speak for myself but even though I reject the defense OS in its entirety I do consider JB admitting that Caylee died on the 16th in Casey's presence as a sign that it probably is true.
Another thing I consider as a possible grain of truth in the OS is JB slipping that it could have been early afternoon and changing it to early morning hours. It sounds like he couldn't keep the real story and the fake story apart for a second. So, did she die early afternoon?