$d = '20110327';

s/\;$d/$c++/ge for <DATA>;

print "$c\n";

__DATA__
13645722;20110327203202.0Z;20140211204731.0Z
14947374;20110327203202.0Z;20140220135320.0Z
15962660;20110327203156.0Z;20131106113716.0Z
17480884;20110327212821.0Z;20131211143804.0Z
13054554;20110327203141.0Z;20110627162959.0Z
13645722;20110427203202.0Z;20140211204731.0Z
14947374;20110527203202.0Z;20140220135320.0Z
15962660;20110127203156.0Z;20131106113716.0Z
17480884;20110627212821.0Z;20131211143804.0Z
13054554;20110227203141.0Z;20131205162959.0Z