$re = '/(?!\S{13})(?:COT|MED)[ABCD]?-?\d{1,4}(?:[JK]+\d*|(?: [A-Z]+)?)/';
$str = 'MED-123
COTA-1224
MED4
COTB-892K777
MED-33 DDD
MED-234J5678
COT-1111J11111111111111';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php