I'm not so sure you should be doing all of the work inside of a regular expression. Here are two ways to do what you're after:

Example #1

open(my $fh, "<", $ARGV[0]) or die "\n$0 Error => $^E\n";
my $data = do { local $/; <$fh> };
close $fh;
my @records = split /(?=\n\d+\s+)/, $data;
# Now each item of @records has the lines you're looking for
[download]

open(my $fh, "<", $ARGV[0]) or die "\n$0 Error => $^E\n";
my (@records,$rec);
while (<$fh>) {
   unless (/^\d+\s+/) {  $rec .= $_; next }
   push @records, $rec if $rec; $rec = $_
}
push @records, $rec if $rec;
close $fh;
# Now each item of @records has the lines you're looking for
[download]

Can you guess which example I like best? :-)

You can use various print statements if you don't want to populate an array of course.