And sometimes they could arrive out of order, because if the disc at the top of your queue is out of stock they will send you the second disc in your queue and so on. FWIW, I've personally rented at least 6 or 7 full seasons of various shows in the last 9 months and haven't received a single disc out-of-order.
It wouldn't matter if I did, since I rip them all for later viewing anyway, but I digress...