If you have access to a resource and you cannot locate it in the Holdings Management site using the Titles tab, then you can add it to your collection as a custom resource using the Create a Custom Resource link on the Titles tab or by using the Upload option. It will be considered a custom title for which you would then maintain all of the desired details.
However, consider that it may be listed using a different variation of the name. Remember that the Knowledge Base includes resources to which other institutions would also subscribe, so if it is a rather common resource, then it is likely to be in the Knowledge Base. Therefore, if you are continuing to experience issues locating the title it is recommended that you contact Customer Satisfaction (email@example.com) for assistance.