You use Import Catalog when the media in question is in your Internal Database
You use Import when the media is NOT in the Internal database
Import generally does a more complete job, but you have to import the media in the same order it was used for back up. This can be obtained from the 'media.log' file, or by running
omnidb -session [session_id] -media Do not include the [ ] marks
If using Import Catalog, the order of the Import is not important
I generally prefer using the method of Exporting the media, and Importing it again
After Importing Media, especially if session protection has expired, get the Session_id of the Imported session, go to the Internal Database context of the GUI, expand session, find the session you just Imported, right-click on it and set Protection, I would recommend to Permanent, or, at least for a long time so Daily Maintenance does not delete the Catalog
Try to avoid importing at close to Noon, when Daily Maintenance is due to run