How do I create a term for every value of a post meta?

Question

I have some information stored in post meta that I'd like to convert to terms. I'd like to create a term in a custom taxonomy for every meta value with a particular key.

I need to loop through ALL posts, gathering all values of the metavalue key.

I'm thinking the code will be like this, I'm just not sure the syntax exactly.

<?php
$all_posts_with_release_year = new WP_Query( [
    'post_type' => 'release'
] );
if ( $all_posts_with_release_year->have_posts() ) {
    while ( $all_posts_with_release_year->have_posts() ) {
        $all_posts_with_release_year->the_post();
        $post_id = get_the_ID();
        $release_year_value = get_post_meta( $post_id, 'wpcf-release-year', true );
        //Check to see if a taxonomy term with that name exists.
        if ($release_year_value exists as $taxonomy_term){
           select $taxonomy_term for $post_id;
        }else{
           create $taxonomy_term with $release_year_value;
           select $taxonomy_term for $post_id;
        }
    }
}

EDIT: I realize I have two smaller questions.

1. How to create a taxonomy term in a foreach loop
2. How to select a taxonomy term for a post in a foreach loop

I'm going to see about the answers to these on the site and will post an answer if I find it, so that someone who hasn't broken this bigger question down into the smaller ones yet can find help.

Thanks so much!