Inky, I was giving a chance for the others to respond with their thoughts. I certainly didn't mean to ignore your question. The answer is: Shouldn't be a problem. Submit what you need help with or want feedback on at the time, regardless of what you've submitted previously. It wouldn't even have to be the opening chapters.
If anyone does submit non-opening chapters, you may wish to give us a short description of what's come before, though.
If anyone does submit non-opening chapters, you may wish to give us a short description of what's come before, though.