Ejecting physical media from your library does not remove it from the media pool. if you want the tapes to no longer be visible in the media pool, you must right-click on a media and export it. This removed the media, and all session information associated with it from the Internal Database, so, be careful how you do this. You would not be able to REstore until you Import the Media again
If media is still protected, it must be ReCycled to remove protection before the Export