At first glance I don't see why something like

if ($month > 11)
{
    my $gap = int($month/12) ;
    $year += $gap ;
    $month -= 12*$gap ;
}
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out of the unless ($Options{no_range_check}) braces in Local.pm timegm function shouldn't make it, at least for months over 11... For negative months it's a bit more complex...

Gu