Robin - Here are some possibilities, below.
        Be sure to check your dsmerror.log and server Activity Log for
anomalies.  You might try a 'dsmc i' on such a test file and see what
gives.

Backed-up files missing                 You believe that certain
files should
                                        have been backed up from a
client file
                                        system, but when you later
perform a
                                        query or attempt a restoral,
they aren't
                                        evident. Several possibilities:
                                        - They were excluded from
backup.
                                        - The type of backup being
done on your
                                          system is -INCRBYDate and
the file was
                                          introduced to the file
system via a
                                          method which preserved its
old
                                          datestamp.
                                        - They cannot be seen
because the
                                          directory containing them
expired from
                                          TSM storage and the GUI
you are using
                                          cannot show them because
the directory
                                          is missing.
                                        - The files went Inactive
and were
                                          expired some time ago.
                                        - The files are quite busy
and cannot
                                          get backed up with your
prevailing
                                          client CHAngingretries value.
                                        Don't use a GUI to check for
such files:
                                        use the CLI, as in 'dsmc
query backup
                                        -inactive FileName'.

  Richard Sims