use strict;
use warnings;

my $regex_orig = qr{(?:^.* Electronic \s* Signature\(s\)\n)?
   (?:.* Signed \s* By:.* \n?
      (?:Date: \s* \S .*\n
        |Date:\n
           (?:\s* \S .*\n)+
      )+
   )+
   (.*)
   (?:Entered \s* By:.*)?}xmi;

my $regex_fixed = qr{(?:^.* Electronic \s* Signature\(s\)\n)?
   (?:.* Signed \s* By:.* \n?
      (?:Date: \s* \S .*\n
        |Date:\n
      )+
   )+
   (?:\s* \S .*\n)+
   (?:Entered \s* By:.*)?}xmi;

my $input_data = "Electronic Signature(s)
Signed By:
Date:
Myself, Me 08/01/2014 12:18:41 PM
Myself, Me 08/01/2014 12:18:42 PM
Them
Entered By: Myself, Me on 08/01/2014 8:44:43 AM";

my $input_data2 = "Electronic Signature(s)
Signed By: Myself, Me
Date: 08/01/2014 12:18:41 PM
Signed By: Myself, Me
Date: 08/01/2014 12:18:42 PM
7/31/2014 3:51:51 PM Version Signed By:
Date:
Myself, Me 7/31/2014 4:07:12 PM
Myself, Me 7/31/2014 4:07:12 PM
7/31/2014 2:40:50 PM Version Signed By:
Date:
Myself, Me 7/31/2014 2:41:24 PM
Entered By: Myself, Me on 08/01/2014 8:04:05 AM";


my $found;

print "-- orig:\n";
if ($input_data2 =~ $regex_orig) {
    $found = substr($input_data2, $-[0], $+[0]-$-[0]);
}

print $found . "\n\n\n";

print "-- fixed:\n";
if ($input_data2 =~ $regex_fixed) {
    $found = substr($input_data2, $-[0], $+[0]-$-[0]);
}

print $found . "\n";