You have to train grappling (from standing AND ground) by themselves, then you have to add strikes, and then add a knife into the mix. It's all good training.
I believe that if you're truly into training for self defense, you HAVE to add knife training to your program - if nothing more than to maintain some awareness of what can happen.
The good thing is that, the grappling game (at least from standing) doesn't change all much when a knife has entered the picture. Truthfully, the ground game doesn't change all the much either once its been fully thought-out.