Maybe it depends what the niggling symptom is. And it is probably a question you should be asking your neurologist when you see him/her.
I’m sure that many people have had MS for way longer than it was first thought. So it’s certainly possible that your MS goes further back in time than you’ve recognised so far.
With me, I absolutely know when I had my first symptom. I remember asking people I worked with if having a numb finger was something they’d see a doctor about. And I remember when it was, partly because it was in my first couple of months into a new job, and also, it coincided with my 30th birthday.
Btw, I wouldn’t be too quick to get your neurologist to say that your MS is SP. Unless the neurologist is absolutely certain, they can keep calling it RR, which means you qualify for DMDs. (Assuming you are taking a DMD that is.) And you could still be RR, just with long gaps between relapses.
It is very tempting to start thinking you are SP. Many of us (me included) thought I had become progressive long before I actually was. Then had an absolute humdinger of a relapse. So in my opinion, the longer you are classed as RR and continue to take DMDs, the better. Unless there is clear evidence of progression and an end to relapses. Don’t forget that some people are progressive but continue to have relapses as well.