Well unless you parade it around, there is no way to prove when you built out your pre Oct 2013 lower. So this means that you are not restricted to hbar and the other crap that comes with post Oct 2013. Even if you simply build out your lower pre Oct all you need to do is mount it to a "assault rifle" configured upper and it would be (in theory) grandfathered in. Pre Oct lowers do have a little more wiggle room than post.Maybe I'm missing something, but I don't really see what difference it makes.