It needs a little more work than that. Replace the fake up loop and preceding line with:

    my $lastToAdd = -1;

    # Fake up present flag for +/- 8 lines around real data
    for my $pip (0 .. $#$origin) {
        next if $pip > $lastToAdd and ! defined $origin->[$pip];

        if ($pip <= $lastToAdd and ! defined $origin->[$pip]) {
            @{$origin->[$pip]}[0 .. $numColumns - 1] =
                ('', $oKey, $pip + 1, ('') x $numColumns);
            next;
        }

        my $first = $pip > 8 ? $pip - 8 : 0;
        
        for my $index ($first .. $pip) {
            next if defined $origin->[$index];
            
            @{$origin->[$index]}[0 .. $numColumns - 1] =
                ('', $oKey, $index + 1, ('') x $numColumns);
        }
        
        $lastToAdd = $pip + 8;
    }
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The problem of course is that the finish point needs to be reset each time a new real line is found.