I'm totally guessing here, so don't take this as authoritative...
I think that what normally determines whether you go to PLC juniors or combined initially is your class standing. However, if you figured out a way to graduate earlier than you originally intended, you wouldn't necessarily change programs. For example, if you had 3 semesters left of college the summer you wanted to start OCS, you'd go to PLC juniors. However, if you figured out some way to get enough credit to graduate after 2 semesters instead of 3 (and I can think of a few, although I won't get into it here), you'd still probably go through PLC seniors instead of starting the 10-week program again. I don't know why you'd want to do this, though. In my opinion, 10 weeks is the way to go. I'd ask your OSO. Also, if you could explain your situation in a little bit more detail to give some sense of why you're asking, that could help someone here get you a better answer.