I've seen previous SNA/NFO threads where people were able to get their OCS dates moved around and in some cases get an earlier class date. However I've also seen the other end of the spectrum where people have gotten even later OCS dates than they were originally assigned. If I had to guess, it comes down to available spots in class rosters and accession numbers. You can ask your OR to get you shipped out to the earliest class possible but it probably just comes down to luck and availability. I know some of us probably want to get to OCS as soon as possible, myself included, but I'm still living with the mindset that if I get a ProRec-Y that I'm probably not going to be shipping for another ~6 months. It sucks, but there's not much we can do about it besides filling your time with work, studies, or whatever gets you to the next sleep.