You don't give us enough information here, 2 years for a year is not enough, unless you are dealing with really, really old newsletters!

But I will assume you are dealing with recent issues, 1951 to 2051 and use a windowing technique. Note that I cannot go from 1930 to 2030 because I think it is patented (and I should stop reading /.).

I would advise you to simply rename all the files, that will save you trouble down the road.

#!/bin/perl -w;
use strict;
foreach my $file (glob( "files/*")) # put the files dir here
  { rename( $file, correct( $file)) 
      or die "could not rename $file into " . correct( $file) . ": $!"
+;
  }
sub correct 
  { my $date= shift; 
    my ($month, $year)= $date=~ /^(\d\d)(\d\d)/; 
    if( $year > 50) { $year +=1900} 
    else { $year+=2000}; 
    return $year.$month;
  }
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Then you can just sort file names alphabetically and you will be ok.

If you don't want to rename the files you can use a merlyn-ian transform, also known outside of PM as the Schwartzian Transform:

my @sorted_filenames= map  { $_->[0] }
                            sort { $a->[1] cmp $b->[1] }
                            map  { [$_, correct($_)] } 
                            glob( "files/*");
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