A method to audit portable cassettes removeably disposed in a data storage library comprising a plurality of storage slots, a plurality of portable cassettes removeably disposed in one or more of said plurality of storage slots, and a pass-through accessor comprising a moveable fixturing apparatus, wherein the pass-through accessor is moveably disposed in said data storage library. The method disposes the pass-through accessor adjacent a first one of said plurality of storage slots, removes a first portable cassette from the first storage slot, and attaches the first portable cassette to a first fixturing assembly disposed on the fixturing apparatus. The method then removes a second portable cassette from the first storage slot, and attaches the second portable cassette to a second fixturing assembly disposed on the fixturing apparatus.