@TyW Thanks for the helpful post. It looks like your original post uses the term “cart” in many places where it should say “checkout”.
Using a permalink in the way you state:
/cart/{variant_id}:{quantity}
does not load anything into the cart cookie for Shopify as a user would think by reading “pre-load cart.”
Rather using this permalink initiates a new checkout with the items in the URL.
Consider reviewing and updating your original post to state that "Use permalinks to pre-load the checkout"
If Shopify added a feature to add the checkout permalink’s items to the cart cookie then your post would be closer to accurate. Here’s more on that issue: