What database state changes happen after a post is manually “updated” with no changes?

To answer my own question, WordPress does not appear to make any changes to the database after a post “Update” that contained no changes. Any changes that happen should be the result of a theme or plugin.

However, the Advanced Custom Fields (ACF) plugin does. Specifically, if ACF fields are set (such as through WP All Import) without also setting the ACF field key reverence, it appears that a click of the “Update” button will add these field key references.

When I attempted to add field key references to my import, I still had issues. Therefore, I found the easiest solution (instead of clicking “Update” on several hundred posts) was to run the following:

function bulk_update_posts() {

    $args = array(  'post_type'=>'post', // Change 'post' if you're using pages or a CPT
                    'posts_per_page'   => -1,
                    'post_status' => array('publish', 'future') // Includes published AND scheduled posts
    );

    $all_posts = get_posts($args);

    foreach($all_posts as $key => $one_post){
        $meta_values = get_post_meta( $one_post->ID);
        foreach($meta_values as $meta_key => $meta_value ){
            update_field($meta_key, $meta_value[0], $one_post->ID);
        }
    }
}
add_action( 'init', 'bulk_update_posts' );
//add_action( 'wp_loaded', 'mass_update_posts' );