I have never heard of stages. I have heard of 4 types. There is relapsing remitting MS (RRMS); this is when you have quiet periods followed by relapses or flares. There is secondary progressive MS (SPMS); this is when there is steady progression with or without periods of acute flaring. There is primary progressive MS (PPMS); this is when a person starts with steady progression with or without flares. There is also progressive relapsing MS (PRMS); this is when a person has a more aggresive progression with flares but never remission.
85% if people are diagnosed with this form. After ten to twenty years, many people with RRMS will transition to SPMS (could this be what you mean by second stage MS?). about 10% if people are diagnosed with PPMS. The last form, PRMS is a rare form; only about 5% are diagnosed with this one.
Your doctor should be able to tell you what kind of MS you have. Most treatments to slow progression are targeted for RRMS. If you are taking avonex, rebif, betaseron, or copaxone, then you are probably RRMS. If you have times when your symptoms are stable (even the permanent ones) then you are RRMS. If you constantly progress with few flares then you are one of the more progressive forms. The progressive forms are marked by no remission.