Why did I not get both chapter 6 cgs?
I haven't gotten chapter 6 cgs either.
Depending on which answer you pick in Chapter 6, Episode 5, you get either the CG with Noritsune and Sohma fighting, or with Yoshitsune and Noritsune fighting. You can't get both CG's, so you have to replay the whole Noritsune-Route to get the other CG.
I remember I got both cgs at the same time.