Typical 3rd-party website, doesn't display sensible things like kuid numbers. However I notice a lot of the assets have links to the DLS, so if they are on the DLS your Content Manager should already list those ones. That means the missing ones are probably those on the website without a DLS link. Just download that lot and see if the missing kuids are in amongst them. Otherwise an email to the site/asset owner might be worth it.