Image source: http://www.nofavt.org/imgs/Conference09.jpg
Book publishers sometimes send partial orders of textbooks to schools if they
do not have enough in stock, or if there is a very large order that will come
in several shipments. If the school ordered 500 history books, they might receive
200 at first and then 300 later, or 300 at first and then 200 later. Either
way, they will eventually receive the right amount from their order.