Ok, let me see if I've got this straight. Brown and Agouti are variations of the same modifier, but Brown doesn't restrict black to the points, and 'fades' the soft points? So, would a "brown" horse be able to throw a true buckskin with a cremello? It doesn't sound like it, more like you'd get the sooty variations? Is that correct?
Brown can often restrict black in ways that make it mimic bay. This shows a few of the variations of brown that are "normal" for brown. Bear in mind, this picture is fairly old, and since then lots of other horses have been tested positive too. It's just really hard to google "tested brown horse" and get any sort of meaningful results lol.