Check out these adult Broad-winged Hawk tails. Notice that the outer tail feathers on the first 3 birds is juvenile-like? These are actually adult feathers, and this is typical of Broad-wingeds (and adults of other species, i.e male Kestrel, Cooper's, Sharpie, many RT's, etc.), where the outer tail feathers are slightly different in pattern. We know these are not retained juvenile feathers since these feathers are not the last ones to drop out. Check out the bottom pic, and note how those outer tail feathers are similar to the rest of the tail…just goes to show that almost no rule is 100%, but if you know what to look for, you won't get fooled. The tail in the top photo is less "white and black" than the other adults…another oddity that occurs sometimes.
Also, in some birds (such as Northern Harrier), the central tail feathers differ than the rest of the tail...may be another post.