<?php
     $a = 'Annex II/8Annex III/101';
     preg_match_all('/bII/b/', $a, $matches);
     print_r($matches[0]);
 ?>

$a = 'Annex II/8Annex III/101';
 preg_match_all('#bII/d(?=D)#', $a, $matches);
 print_r($matches[0]);

II/8