Your answer for the 'actual question' works. Thankyou for that. To address your first point I have done the following:

 if ($file_in_question =~ /^(\d{4})/){
    $year = $1;
  }
  else {
    next;
    }
[download]

Also I would like to say that BrowerUK's explanation offered in the post you refer to, I believe, is very well written. I would encourage anyone here to read it through.