>    If so, how can a volume with only 14.1 percent utilized be 'Full'?

Because, physically, it really is full.  Viz.:

Full                                    Typical status of a tape in a 'Query
                                        Volume' report, reflecting a sequential
                                        access volume which has been used to the
                                        point of having filled. To ensure good
                                        rotation amongst tapes in your storage
                                        pool, *SM thereafter maintains the
                                        "Full" state as Pct Util drops with the
                                        expiration of files on the tape, which
                                        also reflects the reality of some of the
                                        files on the tape having been only
                                        logically deleted: that is, in real,
                                        physical terms, the tape is still full
                                        as per having been written to the End Of
                                        Tape marker. (The definition of serial
                                        media is that you cannot perform updates
                                        into the midst of the medium.) Hence,
                                        the volume will retain the "Full" status
                                        until either all files on it expire, or
                                        you reclaim it at a reasonably low
                                        percentage.