Only thing I can think of that prevents that, is maybe other hunters don't know exactly what the bros have done but just a general idea. I don't know if I even buy that however, because you'd think the network of hunters, people would find out through someone, etc. It'd be a huge plot hole if hunters knew of the Winchesters friends (as mentioned last night) but not what they do. But then again, you never hear Sam or Dean talk about other hunters' cases except for when they are talking along the lines of "oh well we met him at so and so place, working on the whatever case" (also mentioned last night.)
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