So, this is a two-for-one bug where when a limited item is bought too quickly the serial gets duplicated (multiple of the same serial exist) and then subsequent serials do not exist.
Case in point, the newest limited item has spawned NINE #1 serials, followed by #2 to #9 not existing. #10 does exist.
Account is here: https://www.roblox.com/users/208540854/inventory/#!/accessories