Use the GUID field to maintain old URL redirects

rh-404-overrides.php

<?php
function rh_404_overrides() {
	global $wp_query, $wpdb;
	
	if( $wp_query->is_404 && isset( $wp_query->query_vars['pagename'] ) && !empty( $wp_query->query_vars['pagename'] ) ) {
		$query = "SELECT `ID` FROM `" . $wpdb->posts . "` WHERE `guid` LIKE '%" . $wp_query->query_vars['pagename'] . "%' LIMIT 0,1;";
		$post_id = intval( $wpdb->get_var( $query ) );
		
		if( $url = get_permalink( $post_id ) ) {
			wp_redirect( $url, 301 );
			die();
		}
	}
}
add_filter( 'template_redirect', 'rh_404_overrides' );