previous_post_link/next_post_link not putting all posts in order

I have inherited a site and the previous developer has created a post type. On the main page for this post type there is a list of all the businesses which is listed in the correct order. when you click on one of the businesses it opens a page that gives a summary of each business. At the top of each one of these pages is where the previous_post_link/previous_post_link are located. The issue is that there are about half a dozen of these businesses that are out of order, they are being placed either at the beginning or at the end. Also note that I created a brand new post to test and it to was placed at the end, out of order.
I had thought that perhaps the taxonomy was incorrect and that multiple categories are being used and that was causing the issue so I found something that I thought might help but alas it did not.

**single.php**

<div class="container_16 nested" id="post-nav-links">
            <?php $mam_global_stay_in_cat = ($_GET['stayincat']) ? $_GET['stayincat'] : false;
            if ( $mam_global_stay_in_cat ) { ?>
                <div class="col_8 post-nav-button"><p>Previous:</p><?php previous_post_link('? %link','%title',true) ?></div>
                <div class="col_8 post-nav-button"><p>Next:</p><?php previous_post_link('%link ?','%title',true) ?></div>
            <?php } else { ?>
                <div class="col_8 post-nav-button"><p>Previous:</p><?php previous_post_link('? %link') ?></div>
                <div class="col_8 post-nav-button"><p>Next:</p><?php next_post_link('%link ?') ?></div>
            <?php } ?>
        </div>

**functions.php**

function mam_get_previous_post_join_filter ( $join, $in_same_cat = false, $excluded_categories = '' ) {
           global $mam_global_stay_in_cat;
           if ($mam_global_stay_in_cat) {
           $join = preg_replace('/tt.term_id IN \([^(]+\)/',"tt.term_id IN ($mam_global_stay_in_cat)",$join);
           }
           return $join;
    }
    function mam_get_next_post_join_filter ( $join, $in_same_cat = false, $excluded_categories = '' ) {
           global $mam_global_stay_in_cat;
           if ($mam_global_stay_in_cat) {
           $join = preg_replace('/tt.term_id IN \([^(]+\)/',"tt.term_id IN ($mam_global_stay_in_cat)",$join);
           }
           return $join;
    }
    function mam_previous_post_link_filter ($link='') {
          global $mam_global_stay_in_cat;
          if ($mam_global_stay_in_cat && $link) {
          $link = mam_add_query_arg('stayincat',$mam_global_stay_in_cat,$link);
      }
          return $link;
    }
    function mam_next_post_link_filter ($link='') {
        global $mam_global_stay_in_cat;
        if ($mam_global_stay_in_cat && $link) {
            $link = mam_add_query_arg('stayincat',$mam_global_stay_in_cat,$link);
        }
        return $link;
    }
     function mam_add_query_arg ($key,$value,$link) {
        if (strpos($link,'href')) {
        $hrefpat = '/(href *= *([\"\']?)([^\"\' ]+)\2)/';
        } else {
        $hrefpat = '/(([\"\']?)(http([^\"\' ]+))\2)/';
        }
        if (preg_match($hrefpat,$link,$matches)) {
        $url = $matches[3];
        $newurl = add_query_arg($key,$value,$url);
        $link = str_replace($url,$newurl,$link);
        }
        return $link;
    }

        add_filter('get_previous_post_join','mam_get_previous_post_join_filter');
        add_filter('get_next_post_join','mam_get_next_post_join_filter');
        add_filter('previous_post_link','mam_previous_post_link_filter');
        add_filter('next_post_link','mam_next_post_link_filter');

**Post_type**

register_post_type('posts_firms',
            array(
                'label' => 'Member Firms',
                'description' => '',
                'menu_icon' => 'dashicons-groups',
                'public' => true,
                'show_ui' => true,
                'capability_type' => 'post',
                'hierarchical' => true,
                'rewrite' => array( 'slug' =>'firms'),
                'query_var' => true,
                'supports' => array(
                                'title',
                                'editor',
                                'excerpt',
                                'post-formats')
                                ) );

**taxonomy**
register_taxonomy( 'cities', 'posts_firms', $args );

   $labels = array(
        'name'              => _x( 'Branches', 'taxonomy general name' ),
        'singular_name'     => _x( 'Branch', 'taxonomy singular name' ),
        'menu_name'         => __( 'Branches' ),
        'search_items'      => __( 'Search Branches' ),
        'all_items'         => __( 'All Branches' ),
        'parent_item'       => __( 'Parent Branch' ),
        'parent_item_colon' => __( 'Parent Branch:' ),
        'edit_item'         => __( 'Edit Branches' ),
        'update_item'       => __( 'Update Branches' ),
        'add_new_item'      => __( 'Add New Branch' ),
        'new_item_name'     => __( 'New Branch Name' ),
    );

    $args = array(
        'hierarchical'      => true,
        'labels'            => $labels,
        'show_ui'           => true,
        'show_admin_column' => true,
        'query_var'         => true,
        'rewrite'           => array( 'slug' => 'branch' ),
    );

   register_taxonomy( 'branches', 'posts_firms', $args );

   $labels = array(
        'name'              => _x( 'Country', 'taxonomy general name' ),
        'singular_name'     => _x( 'Country', 'taxonomy singular name' ),
        'menu_name'         => __( 'Country' ),
        'search_items'      => __( 'Search Countries' ),
        'all_items'         => __( 'All Countries' ),
        'parent_item'       => __( 'Parent Country' ),
        'parent_item_colon' => __( 'Parent Country:' ),
        'edit_item'         => __( 'Edit Countries' ),
        'update_item'       => __( 'Update Branches' ),
        'add_new_item'      => __( 'Add New Country' ),
        'new_item_name'     => __( 'New Country Name' ),
    );

    $args = array(
        'hierarchical'      => true,
        'labels'            => $labels,
        'show_ui'           => true,
        'show_admin_column' => true,
        'query_var'         => true,
        'rewrite'           => array( 'slug' => 'country' ),
    );

   register_taxonomy( 'countries', 'posts_firms', $args );

   $labels = array(
        'name'              => _x( 'Regions', 'taxonomy general name' ),
        'singular_name'     => _x( 'Region', 'taxonomy singular name' ),
        'menu_name'         => __( 'Regions' ),
        'search_items'      => __( 'Search Regions' ),
        'all_items'         => __( 'All Regions' ),
        'parent_item'       => __( 'Parent Region' ),
        'parent_item_colon' => __( 'Parent Region:' ),
        'edit_item'         => __( 'Edit Regions' ),
        'update_item'       => __( 'Update Regions' ),
        'add_new_item'      => __( 'Add New Region' ),
        'new_item_name'     => __( 'New Region Name' ),
    );

    $args = array(
        'hierarchical'      => true,
        'labels'            => $labels,
        'show_ui'           => true,
        'show_admin_column' => true,
        'query_var'         => true,
        'rewrite'           => array( 'slug' => 'region' ),
    );

I will be more than glad to supply anything else that would be needed. I am really stuck on this strange issue. Thanks in advance. BTW this is a custom site.
The site is interlaw.org issue is in members>find by list>the individual firms is where the previous and next links are.