The simplest solution, but not the most effective would be to just sort a hash of the month and year... check code.

#this is assuming you are in the right directory
#this is not the most efficient way of getting a list of files
foreach (<*.*>) {
   my($month,$year)=split(/\d{2}/,$_);
   $year+=1900;
   #Assuming that year started after 1990
   if($year<90){$year+=100;}
   $NEWSLETTER{$year}{$month} = 0;
}
foreach $y (sort keys %NEWSLETTER) {
   foreach $m (sort keys $NEWSLETTER{$y}) {
      #insert code for what you want to do with the sorted year and mo
+nth....
   }
}
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"The pajamas do not like to eat large carnivore toasters."
In German: "Die Pyjamas mögen nicht große Tiertoaster essen.
In Spanish: "Los pijamas no tienen gusto de comer las tostadoras grandes del carnívoro."