The 'sexual references' from other women are super weird. What could you even say, except, 'well, he's never tried to rape me'? If you were absolutely convinced that he would never try to rape anyone, surely you wouldn't need to be anonymous? You'd say, "I believe NG 100% and consider these to be malicious rumours." You'd surely have to be that confident to make a statement? I can think of two men in my life who I would be 100% confident about - my dad and one of my brothers.
I think whoever these women are, they are hoping to be able to play both sides. (I think one of them is NG's current main girlfriend? Not sure.) Keep in with NG and then if he seems to be falling out of favour, switch sides. You can't do that if you give your name.
If one of them is his current girlfriend, then I imagine she has very little choice but to support him.