Tag query - AWP Facebook question

<?php
  $posttags = get_the_tags();

  foreach($posttags as $tag) {
      if (is_numeric($tag->name)) {
          $unit_number = $tag->slug;
          echo '<p>History of tag ID: ', $unit_number, '</p>';
          $unit_history_args = array('post_type' => 'post',
                'tax_query' => array(
                    array( 'taxonomy' => 'post_tag',
                            'field'    => 'slug',
                            'terms'    => $unit_number,
                            'operator' => 'EXISTS',
                          ),
                 ),
                 );

          $the_query = new WP_Query( $unit_history_args );
          if ( $the_query->have_posts() ) {
              echo '<ul>';
              while ( $the_query->have_posts() ) {
                  $the_query->the_post();
                  printf('<li><a href="%s">%s</a></li>', get_permalink(), get_the_title());
              }
              echo '</ul>';

              /* Restore original Post Data */
              wp_reset_postdata();
          } else {
              // no posts found
          }
      }
 }