Last-minute bookings are, basically, a way to get rid of stock that's still left on the shelf - you might call it distressed stock that simply won't sell without a bargain basement price label.
So far those pieces have included high capacity ammunition magazines for AR-15s and AK-47s, as well as an AR lower receiver, the body of that semi-automatic rifle to which off-the-shelf components like a stock and barrel can be attached.