Thanks for your replies, everyone. I guess there's not a real answer but maybe I'll give it a shot with my doctor. Just curious as to what they expect to see over time on the MRIs.

Seeing these replies though really did reinforce the "treat the patient not the MRI" phrase. Ironic that progression is measured in the RRMS phase as what the MRI says since it seems pretty clear that the transition to SPMS can happen without any kind of real warning on the films. Not that it definitely does happen that way or that everyone will definitely progress, just that it can happen that way.