rewrite pretty urls with php and htaccess, mapping 404 for subpages - php

Question

In .htaccess I have following rules for having page/subpage rewrite.
#Permalinks
RewriteEngine on
<IfModule mod_rewrite.c>
RewriteEngine On
#catch potential subpages first
RewriteRule ^([a-z\-]+)/([a-z\-]+)/?$ index.php?page=$1&subpage=$2 [L]
#
RewriteRule ^([a-z\-]+)$ index.php?page=$1 [L]
</IfModule>
In php I do this:
if (!$_GET) {
//
$page = "home";
$page_title = "General Site Title";
include ("template/index.php");
//
} else if ($_GET['page'] == "words") {
//
$page = "words";
$page_title = "Words Page";
include ("template/words.php");
//
} else if ($_GET['page'] == "about") {
//
$page = "about";
$page_title = "About Page";
include ("template/about.php");
//
} else {
//
header("HTTP/1.0 404 Not Found");
//
include ("template/404.php");
//
exit();
//
}
This works great, for showing 404.php when page doesn't exist.
But what if I want to have 404.php also when page/subpage doesn't exist?
For example I'm planning to have /members page. If someone goes to non existing /members/user1, I need to check DB for existing user, if doesn't exist I should show 404.php but is this correct logic to use in this situation?
p.s. how do I add rewrite /about/ to show same page? currently /about returns 200, but /about/ returns apache page not found.

Answer 1

First of correction in rules to make trailing slash optional in both rules:
RewriteEngine On
RewriteRule ^([a-z-]+)/([a-z-]+)/?$ index.php?page=$1&subpage=$2 [L,NC,QSA]
RewriteRule ^([a-z-]+)/?$ index.php?page=$1 [L,NC,QSA]
Now about checking /members/user1 yes you can check DB for existence of member record and if not found you can return 404 status/page.