1. Create a CPT

2. In functions.php or in a plugin, hook on 'save_post' to perform some calculations upon hitting the Publish button in WP-Admin...

3. Inside the hook's code include some conditional logic that under certain circumstances it will delete the CPT post that is just being created. Ie study the following piece of code:

add_action('save_post', 'import_external_data', 10, 2);
function import_external_data($post_id, $post)
{
    if ($post->post_status == 'publish' && $post->post_type == 'movie') {
        // Check if movie exists
        $movies = get_posts(array(
            'numberposts' => 1,
            'post_status' => 'publish',
            'post_type' => 'movie',
            'meta_key' => 'movie_id',
            'meta_value' => $post->post_content,
        ))[0];

        if (empty($movies)) {
            // Various actions take place here
        } else {
            wp_delete_post($post_id, true);
        }
    }
}

4. Once the post is deleted you are redirected to the stock post type (?post_type=<CPT_slug> part of the URL is gone)