The way to sort first by year, then month, then day,

sort {
    $hashYear{$a} <=> $hashYear{$b}
      or $hashMonth{$a} <=> $hashMonth{$b}
        or $hashDay{$a} <=> $hashDay{$a}
} @unsorted;
[download]

though I haven't seen what the structure of your elements is. That might indicate another approach such as a Schwarzian Transfornm.

After Compline,
Zaxo