Try it like this:

use warnings;
use strict;

chomp( my @horiz = <STDIN> ); 

my @dates = grep length, split /\|/, shift @horiz; 

for my $line ( @horiz ) { 

    my ( undef, $PID, $SID, @flds ) = split /\|/, $line, -1; 

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