Tales of three steel bikes.
97 Kilauea (Columbus Cyber). One day, seven years ago, I parked it carelessly against a low wall and a sudden gust of wind blew it over and as a result of that major accident it lost a chunk of paint from its seatstay. I did nothing to it and seven years later the bare metal has not gone brown. I can only think that there must be elements within the Cyber alloy that act as rust inhibitors.
98 Explosif (Reynolds 853). When I bought it, it had a large number of paint chips, a few of which were brown in the centre, but the great majority white. So primer obviously works well with 853 and the frame was in no great danger but looked tatty. I Kurusted the brown spots and primed and touched in all the marks and the frame now looks fine to me and I believe it is stable.
96 Explosif (Columbus Max). Same tubeset as yours and Messiah’s. When I bought it, there were a large number of stone chips, all of which were brown, no sign of primer, not even on the edge of each chip. I believe the frame must have been primed, as the paint is perfect everywhere else, no bubbles anywhere, but maybe it’s just that primer sticks far better to the top coat than it does to Columbus Max. I have Kurusted each chip and will prime and touch them in presently. I am confident that that will deal with the surface rust and the frame will be stable.
Then you get the other kinds of example like Fat Chance seat tubes, where beautiful though the bikes are and the most artistic paint jobs ever, the bloody fools didn’t incorporate a drain hole into the bottom bracket shell. So if you see bubbling in the paint at the bottom of the seat tube, that’s it, it’s rust from the inside out, the seat tube is gone and you’re going to need to replace it and respray the frame.
My understanding is that surface rust from stone chips can be treated perfectly well with Kurust and will then be stable. I don’t believe it will spread like wildfire at all, but if anybody knows better I’ll be very interested to hear about it.
So basically if your frame was mine (i.e., if I had more money), I wouldn’t be worried about the marks you mention. Why don’t you post some close ups? There are people on here who know a lot more than me and could probably advise you whether there’s any cause for concern.