Handwaving fish.

my @candidate_files = obtain_candidates( ); ## File::Find::Rule, opend
+ir/readdir, ...

my %seen_files;
my @to_delete;

for my $file ( @candidate_files ) {
  ## regex out, use str2date, yadda yadda yadda
  my( $real_file, $date ) = parse_filename( $file );

  if( not exists $seen_files{ $real_file } ) {
    $seen_files{ $real_file } = [ $file, $date ];
  } else {
    my $prior_date = $seen_files{ $real_file }->[1];

    if( $date - $prior_date > 0 ) {
      $seen_files{ $real_file } = [ $file, $date ];
    } else { 
      push @to_delete, $file;
    }
  }
}

process_deletions( @to_delete );
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