I imagine that a revision has been made recently. If old stock has been removed, they'd probably want to take down sales until it is inspected and/or printed (assuming that they don't operate purely on print-on-demand).
More information about formatting options
I imagine that a revision has been made recently. If old stock has been removed, they'd probably want to take down sales until it is inspected and/or printed (assuming that they don't operate purely on print-on-demand).