One quick thing about going through progressions. Don't have a clue if Coker does or doesn't. We know JJ doesn't. But I'll lay odds that 80% plus....or yep, 176/215ths...of the throws made by college quarterbacks, are to the original target they intended to throw to. Most times, it's a matter of the rare occasion when the QB actually recognizes his guy is blanketed like Michael Jackson's kid and he starts scrambling trying to find another guy. But for the most part, college QB's get the snap, step and fire. Receivers have the advantage anyway, knowing exactly where they're going so more often than not, there's going to be a window in which to hit him.
I think it is more to do with pre-snap reads than check downs. A good QB can check down to 3rd and 4th receiver, but most college QB's have a single read. It may be two receivers, but the QB is checking one player. If the corner does this, throw here, if he doesn't do this, throw there. And if both of those are covered, there is a safety valve.
I have rarely seen Auburn read through more than a 2 person route over the past several years.