First and foremost, it is important to recognize that Jamf Pro is not an asset management tool or solution. The reason why is that so much of the asset data in jamf can be manipulated as the device changes hands, it doesn't do a good job of retaining that information easily (nor should it, really), and there are many workflows in which you straight up delete an item from jamf in order to re-enroll it.
You can export any smart search as a csv! Smart Searches are like Smart Groups, but they are only queried when you run the search. For items you are deprecating, unmanaging the device in the JSS will make sure that you do not use a seat license for that machine. You could then create a smart search for "Managed Is Unmanaged" and then export your CSV that way.
