Get label from dynamically generated select option

I use the following code to fill a select with posts from a custom post type:

function form_posttype_field ( $tag, $unused ) {

if ( $tag['name'] != 'seminarnumber' )
    return $tag;

$args = array (
    'numberposts'   => -1,
    'post_type'     => 'seminars',
    'orderby'       => 'title',
    'order'         => 'ASC',
);

$custom_posts = get_posts($args);

if ( ! $custom_posts )
    return $tag;

foreach ( $custom_posts as $custom_post ) {
	$ID = $custom_post->ID;
	if(get_field('seminar_number', $ID)){
		$tag['values'][] = get_field('seminar_number', $ID);
		$tag['raw_values'][] = $custom_post->post_title;  
		$tag['labels'][] = $custom_post->post_title;
	}else{
		 $tag['values'][] = $custom_post->post_title;
		 $tag['raw_values'][] = $custom_post->post_title; 
         $tag['labels'][] = $custom_post->post_title;		 
	}
     

}

return $tag;
}

add_filter( 'wpcf7_form_tag', 'form_posttype_field', 10, 2);

Works great, but there is one thing I can’t get to run.
I fill the value with a short ID of the seminar and the label with the long title.
In HTML this looks like this:
<option value="W34-2017">W34-2017 = Syst. Case Management/Fallmanagement 2017 (ab 05.10.2017)</option>
But I have no idea how to get the long title (= the label) to send it with the email.
I tried to fill $tag[‘raw_values’][] also with the long title and get this with [_raw_seminarnumber], but I always get the short ID (except if I fill $tag[‘values’][] also with $custom_post->post_title, but that’s not what I want … because I want to preselect an option via url parameter and for this the long title would be to long and to error-prone).

Any ideas how to get the label for sending it with the email?