I spoke to one of the staff on Sunday and they said it was completely out of stock. No restocking, all sold out.

My best guess is that there were limited copies of both and the staff, preview pass holders and first day visitors picked them all up.

I'm not surprised. Neither of those books are prone to "overstocking" like the rest of the BBW sale books so I'm guessing BBW just stocked them to drive interest in the sale.