replace 

for my $date (@dates_copy) { 
print "$PID|$SID|",shift(@flds),"|$date\n"; 
} 

with


for my $date (@dates_copy) { 
    my $field = shift(@flds);
    $field = '' unless ( $field );
    print "$PID|$SID|",$field,"|$date\n"; 
}