The option "Item type usage" does not report on item types that are used as named item lists on pages. Step to repro:
- Create a new item type, enable it for all purposes and locations in settings and in restrictions. Add one field to it
- Go to a page, choose Properties, click Advanced then Item Lists
- Set up a named list using the type from #1 and add some data to it
- Go back to the item type under Settings | Item types and click Item type usage.
Expected outcome: the report shows the page from #3 as a place where the type is used
Actual outcome: the report says the type is not in use.
Note: the report works fine when you use the item type as, say, a paragraph.