Anyone can sign up for August now, if there is a seat left. Your August score, if high enough, would confirm your NMSF score. We know kids who took the August SAT as prep for the Oct SAT.
Now, whether you should take a seat when so many kids going into their senior year haven’t gotten a chance to test yet, is another matter. I would think that most everyone needing that score still has already signed up, but I suppose it depends on where you live as to how aware of the the testing issue the population is. Where we live, I’m sure lots of kids aren’t even aware registration has opened.
A bad score won’t hurt you. You just don’t send it. There used to be a few schools that required all your scores to be sent, but I don’t know if any do anymore. You can google this just to make sure.