Got it! So it is only for SMP and Guard/Reserves, makes senseYou can't join and remain in the Guard/Reserves without an MOS. You can't do SMP without being in the Guard or Reserve. 09R is a placeholder MOS during your last couple of years of school that allows you to remain in the Reserve Component (and using their tuition benefits) while you finish up your degree and officer training as an SMP cadet.
Not much more complicated than that.