You could try the Wordpress function status_header()
to add the HTTP/1.1 404 Not Found
header;
So your Code 2 example would be:
function rr_404_my_event() {
global $post;
if ( is_singular( 'event' ) && !rr_event_should_be_available( $post->ID ) ) {
global $wp_query;
$wp_query->set_404();
status_header(404);
}
}
add_action( 'wp', 'rr_404_my_event' );
This function is for example used in this part:
function handle_404() {
...cut...
// Guess it's time to 404.
$wp_query->set_404();
status_header( 404 );
nocache_headers();
...cut...
}
from the wp
class in /wp-includes/class-wp.php
.
So try using this modified Code 2 example in addition to your template_include
code.