Are you looking for a rolling 12 month window? Ie, if we were in October now, would you be looking for the last two months in 2012?

sub filenames {
  my( $base, $year, $month ) = @_;
  return ( ( map { sprintf $base, $year-1, $_ } $month+1..12 ),
           ( map { sprintf $base, $year, $_ } 1..$month ) );
}

print filenames "file_name_%04d%02d\n", 2013, 11;
[download]

Pls see the trailing "\n" in the filename template which is there only for the printing.