As stated, the board can look at as many NCOERs as the deem appropriate.
A "NO" on the front is huge. A very close friend of mine choked a Soldier who was being disrespectful with borderline racial comments. This happened in 2005. Up to that point, he was the "poster child" NCO. With all of his great NCOERs and accomplishments, the one "NO" held him up for 5 more years than it should have. My point is, if he is innocent, he NEEDS to appeal it. That is why the appeal system is there. Not doing something about it will only hurt him in the long run.