When adding API(s) to an Application in the CA API Developer portal, the dropdown list box where the API is selected shows an incomplete list of the available APIs. The list of APIs is sorted alphabetically, so the missing APIs will all be ones that would appear after the existing listed APIs when alpha sorted.
To get to the 'Add APIs' field where this problem presents itself: From the API Developer portal dashboard, select Organizations, then Applications from the left menu. Edit an application by selecting the gear icon, then Edit. Select the API Management tab and scroll to the bottom to see the 'Choose an API' dropdown list box.