Rand, supposedly, got all the memories of his past lives when he molded with Lews Therin. However, he was surprised to discover that killing the DO would be essentially Turning everyone to the Light and would remove all tangible progress. If he had experienced this battle with the DO before, he would have remembered it and would know he could not kill the DO and save humanity. This leads me to believe that Rand's encounter with the DO may have been a unique event thus far in the Turnings of the Wheel, and that potentially even the Drilling of the Bore may have been itself unique. Either way, something special happened this turning that has not happened before, and so the ending we got may be more permanent than previously thought.