At first glance I see that here:

while (defined $dates[0]) {
  my $days = $dates[0];
  my ($year, $month, $day) = Add_Delta_Days(1,1,1, $days - 1);
  @dates = CreateCal($year, $month, @dates);
}
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you are calling Add_Delta_Days. Then you call it again in the CreateCal subroutine with different data.

Is it supposed to do that? Maybe I'm not understanding what you hope to acheive.