The cleanest way to approach this would be to put each tape in the drive then run an inventory and catalog (from the Devices tab) to place each piece of media back into the system.
I think the media will show up in the "Imported" secion of the media set tab because it was technically created with a different installation of BE.
Depending on your overwrite settings, you could move them to a user media set to get around the "overwrite imported media" prompts (if you have that set up).
I'm assuming that even though you reinstalled BE that the data stored on the media is valid. If it isn't, I would also recommend doing an erase operation on each tape you wish to use in your rotation. Basically start with a clean slate.
Hope this helps...