Mine has advanced - 18 years ago I was diagnosed with ulcerative proctitis and now its all the way up my left side and a little around the corner, with patchy spots after that. My last colonoscopy was a year ago and at that time I had no signs of disease (my colon looked normal). But I'm pretty sure with this current flare-up it has spread further as I've been having pain in my left side higher up which I never had in the past. I won't know till my next colonoscopy next year but the flex sig I had in January showed alot of inflamation up to the point they went with that scope.
I kept my disease under control for 10 years which I think prevented it from spreading further. I feel like once you flare up, you always have a chance it will spread the longer you are in the flare.