I was going to say it was possible that he didn't know that he himself had it, but that seems unlikely seeing as he knew about it when Itachi used it.

Check to see what he said when he first used it vs Diedara, I THINK he said something along the lines of "I found something, I want to try a new technique" meaning that he didn't know that he had it before, but he knew about it...

*me going around in an endless circle