Dynamically added text at bottom of article - non searchable by PHP code

Question

I need to move certain articles on my website, all of them, to another unique category. I am using specific phrase which is at bottom of every article, but after code execution, only two articles are moved to new category, not all of them. Also when I search through all posts using native Dashboard-All posts option, it returns only those two articles, not all of them. I assume that is because text is not stored in database, because it shows only when post renders it self on frontend. How can I include dynamically created text into my code?

My code, just for reference:

<?php
// Move to category Breaking News
$target_category_id = 1982;

// Get all posts that contain the search phrase from Syndication
$posts = get_posts(array(
  's' => 'and has been published here with permission',
  'post_status' => 'any',
  'posts_per_page' => -1 // This will retrieve all posts
));

// Loop through the posts and move them to the target category
foreach ($posts as $post) {
  // Remove the post from any existing categories
  $current_categories = wp_get_post_categories($post->ID);
  wp_remove_object_terms($post->ID, $current_categories, 'category');

  // Add the post to the target category
  wp_set_post_categories($post->ID, array($target_category_id), true);
}

EDIT That specific phrase is created dynamically, because I am using WP Broadcast plugin to add text at the bottom of every broadcasted article, but I am not sure is that phrase stored in database or that text is dynamically populated (created) every time post is rendered on frontend.

This is the code I am using to generate message (phrase) at the bottom of every article:

<?php
function broadcasted_from()
{
    // Check that Broadcast is enabled.
    if ( ! function_exists( 'ThreeWP_Broadcast' ) )
        return;
    // Load the broadcast data for this post.
    global $post;
    $broadcast_data = ThreeWP_Broadcast()->get_post_broadcast_data( get_current_blog_id(), $post->ID );
    // This post must be a child. Check for a parent.
    $parent = $broadcast_data->get_linked_parent();
    if ( ! $parent )
        return;

    // Fetch the permalink
    switch_to_blog( $parent[ 'blog_id' ] );
    $blog_name = get_bloginfo( 'name' );
    $permalink = get_post_permalink( $parent[ 'post_id' ] );
    restore_current_blog();

    // And now assemble a text.
    $r = sprintf( 'This article appeared in <a href="%s">%s</a> and has been published here with permission.', $permalink, $blog_name );
    return $r;
}
add_shortcode( 'broadcasted_from', 'broadcasted_from' );

add_filter( 'the_content', function( $content )
{
// Get the broadcasted from text.
$sc_text = do_shortcode( '[broadcasted_from]' );
// Add the text to the content.
$content .= $sc_text;
// Return the expanded content.
return $content;
} );