All I can say, is what I initially went through with Gynecomastia.
I noticed my nipples were on fire and easily chaffed, then I notice a nodule about the size of a marble just behind my nipple.
About 1 month later, the nodules softened, but then I noticed what I call "Girly Mounds" starting to form.
I don't believe I ever noticed any veins starting to appear, but that might be because my heart surgeon used my Mammary Vein for part of my Bypass surgery. Heck, not even sure if that is what anyone else has seen, but if it is, that could explain me not seeing it.