As a small variant, you can calculate a key by 100*year+month, assuming that month will always be two digit at most...

my @sorted = sort {
    ($a =~ /\.([0-9]+)-([0-9]+)\./, 100*$1+$2) 
<=> ($b =~ /\.([0-9]+)-([0-9]+)\./, 100*$1+$2)
} @strings;
[download]

or would it be ok to insert the missing zero?

map { s/-(\d)\./-0\1./ } @strings;
my @sorted = sort @strings;
[download]

(Make sure the regexp does not match elsewhere in your strings.)