You may have added items directly to the projects using the New > Item workflow under the Project tab in Project Editor, rather than from the catalog. You can search for such items across all projects, including archived ones, and view them all in one place.
To search for items that were not added from the catalog, go to Project Explorer and click Find Project Items Not In Catalog under the Reports tab.
You will see the Find Project Items Not In Catalog modal with all non-catalog items across all projects. You will be able to see some details of the items and the projects they are associated with.
You can do the following in the modal.
See both products and labor items, or see only one of them by selecting Include Products and Include Labor Items in the Filter section of the ribbon.
Select an item and click Open Project View to go to the Project Editor of the project it is associated with.
Select products or labor items from a single project and click Update to Catalog to update (add) them to the catalog.
Export the list of items to a CSV or PDF file by clicking Export.