File: wordpress-seo/frontend/class-breadcrumbs.php

Line 164 - 170:
			} elseif ( is_404() ) {
				if ( isset( $options['breadcrumbs-404crumb'] ) && $options['breadcrumbs-404crumb'] != '' )
					$crumb404 = $options['breadcrumbs-404crumb'];
				else
					$crumb404 = __( 'Error 404: Page not found', 'wordpress-seo' );
				$links[] = array( 'text' => $crumb404 );
			}

replace with:
			} elseif ( is_404() ) {

				if ( get_query_var( 'year' ) !== 0 || ( get_query_var( 'monthnum' ) !== 0 || get_query_var( 'day' ) !== 0 ) ) {
					
					if ( "page" == $on_front && !is_home() ) {
						if ( $blog_page && ( !isset( $options['breadcrumbs-blog-remove'] ) || !$options['breadcrumbs-blog-remove'] ) )
							$links[] = array( 'id' => $blog_page );
					}

					if ( isset( $options['breadcrumbs-archiveprefix'] ) )
						$bc = $options['breadcrumbs-archiveprefix'];
					else
						$bc = __( 'Archives for', 'wordpress-seo' );


					if ( get_query_var( 'day' ) !== 0 ) {
						global $wp_locale;

						$links[] = array(
							'url'  => get_month_link( get_query_var( 'year' ), get_query_var( 'monthnum' ) ),
							'text' => $wp_locale->get_month( get_query_var( 'monthnum' ) ) . ' ' . get_query_var( 'year' )
						);
						global $post;
						$original_p = $post;
						$post->post_date = sprintf("%04d-%02d-%02d 00:00:00", get_query_var( 'year' ), get_query_var( 'monthnum' ), get_query_var( 'day' ) );
						$links[] = array( 'text' => $bc . " " . get_the_date() );
						$post = $original_p;

					} else if ( get_query_var( 'monthnum' ) !== 0 ) {
						$links[] = array( 'text' => $bc . " " . single_month_title( ' ', false ) );
					} else if ( get_query_var( 'year' ) !== 0 ) {
						$links[] = array( 'text' => $bc . " " . get_query_var( 'year' ) );
					}
				}
				else {
					if ( isset( $options['breadcrumbs-404crumb'] ) && $options['breadcrumbs-404crumb'] != '' )
						$crumb404 = $options['breadcrumbs-404crumb'];
					else
						$crumb404 = __( 'Error 404: Page not found', 'wordpress-seo' );
					$links[] = array( 'text' => $crumb404 );
				}
			}




File: wordpress-seo/frontend/class-frontend.php

Line 355-359:
		} else if ( is_404() ) {
			$title = $this->get_title_from_options( 'title-404' );

			if ( empty( $title ) )
				$title_part = __( 'Page not found', 'wordpress-seo' );

replace with:
		} else if ( is_404() ) {
			
			if ( get_query_var( 'year' ) !== 0 || ( get_query_var( 'monthnum' ) !== 0 || get_query_var( 'day' ) !== 0 ) ) {

				if ( get_query_var( 'day' ) !== 0 ) {

					global $post;
					$original_p = $post;
					$post->post_date = sprintf("%04d-%02d-%02d 00:00:00", get_query_var( 'year' ), get_query_var( 'monthnum' ), get_query_var( 'day' ) );
					$title_part = sprintf( __( '%s Archives', 'wordpress-seo' ), get_the_date() );
					$post = $original_p;
				}
				else if ( get_query_var( 'monthnum' ) !== 0 ) {
					$title_part = sprintf( __( '%s Archives', 'wordpress-seo' ), single_month_title( ' ', false ) );
				}
				else if ( get_query_var( 'year' ) !== 0 ) {
					$title_part = sprintf( __( '%s Archives', 'wordpress-seo' ), get_query_var( 'year' ) );
				}
				else {
					$title_part = __( 'Archives', 'wordpress-seo' );
				}
			}
			else {
				$title = $this->get_title_from_options( 'title-404', array( 'term404' => get_query_var( 'pagename' ) ) );

				if ( empty( $title ) )
					$title_part = __( 'Page not found', 'wordpress-seo' );
			}



File: wordpress-seo/inc/wpseo-functions.php

Line 110-111:
		'term_id'       => '',
	);

replace with:
		'term_id'       => '',
		'term404'		=> '',
	);


Line 173-174:
		'%%caption%%'                   => $r->post_excerpt,
	);

replace with:
		'%%caption%%'                   => $r->post_excerpt,
		'%%term404%%'			=> sanitize_text_field ( str_replace( '-', ' ', $r->term404 ) ),
	);



File: wordpress-seo/admin/pages/metas.php

Line 298-299:
			</tr>
			<tr>

replace with:
			</tr>
			<tr>
				<th>%%term404%%</th>
				<td>' . __( 'Replaced with the slug which caused the 404', 'wordpress-seo' ) . '</td>
			</tr>
			<tr>