WordPress year/issue-based magazine URL structure…how did they do this?

I’ve seen a lot of almost answers but nothing definitive, so here I am.

I’m trying to structure my WP permalinks as http://magazine.pomona.edu does. The site is organized as http://example.com/%volume_year%/%volume_issue%/%postname%/. Example: http://magazine.pomona.edu/2012/fall/a-carefully-calculated-caper/

I’m having problems figuring out a permalink structure that doesn’t give 404s or 400s. I created two custom taxonomies, ‘volume_year’ & ‘volume_issue’. I changed my permalink structure to reflect these (/%volume_year%/%volume_issue%/%postname%/) and checked the appropriate terms within the post admin (2012 & Fall).

However, when I attempt to view the post, which should be at http://example.com/2012/fall/lost-and-found/. I get a 400 Bad Request error and my URL is http://example.com/%volume_year%/%volume_issue%/lost-and-found/. Obviously, the placeholders are not being converted to terms. What am I missing, and/or does anyone have a better way to do it?

Here’s my code, fwiw:

$labels[0] = array(
            'name'                       => 'Year',
            'singular_name'              => 'Year',
            'menu_name'                  => 'Year',
            'all_items'                  => 'All Years',
            'parent_item'                => 'Parent Year',
            'parent_item_colon'          => 'Parent Year:',
            'new_item_name'              => 'New Year Name',
            'add_new_item'               => 'Add New Year',
            'edit_item'                  => 'Edit Year',
            'update_item'                => 'Update Year',
            'separate_items_with_commas' => 'Separate years with commas',
            'search_items'               => 'Search years',
            'add_or_remove_items'        => 'Add or remove years',
            'choose_from_most_used'      => 'Choose from the most used years',
        );

        $rewrite[0] = array(
            'slug'                       => 'volume_year',
            'with_front'                 => false,
            'hierarchical'               => true,
        );

        $args[0] = array(
            'labels'                     => $labels[0],
            'hierarchical'               => true,
            'public'                     => true,
            'show_ui'                    => true,
            'show_admin_column'          => true,
            'show_in_nav_menus'          => true,
            'show_tagcloud'              => true,
            'query_var'                  => 'volume_year',
            'rewrite'                    => $rewrite[0],
        );

        register_taxonomy( 'volume_year', array('post'), $args[0] );

        $labels[1] = array(
            'name'                       => 'Issue',
            'singular_name'              => 'Issue',
            'menu_name'                  => 'Issue',
            'all_items'                  => 'All Issues',
            'parent_item'                => 'Parent Issue',
            'parent_item_colon'          => 'Parent Issue:',
            'new_item_name'              => 'New Issue Name',
            'add_new_item'               => 'Add New Issue',
            'edit_item'                  => 'Edit Issue',
            'update_item'                => 'Update Issue',
            'separate_items_with_commas' => 'Separate issues with commas',
            'search_items'               => 'Search issues',
            'add_or_remove_items'        => 'Add or remove issues',
            'choose_from_most_used'      => 'Choose from the most used issues',
        );

        $rewrite[1] = array(
            'slug'                       => 'volume_issue',
            'with_front'                 => false,
            'hierarchical'               => true,
        );

        $args[1] = array(
            'labels'                     => $labels[1],
            'hierarchical'               => true,
            'public'                     => true,
            'show_ui'                    => true,
            'show_admin_column'          => true,
            'show_in_nav_menus'          => true,
            'show_tagcloud'              => true,
            'query_var'                  => 'volume_issue',
            'rewrite'                    => $rewrite[1],
        );

        register_taxonomy( 'volume_issue', array('post'), $args[1] );