Magento2 Event 'customer_register_success' or 'customer_login' for adding product to Wishlist

I’ve created Guest Wishlist and now I am trying to add products from cookie to a Customer Wishlist.

Problem is that if I observe ‘customer_register_success’ wishlist is not created until new customer is fully logged in.

If I observe ‘customer_login’ then problem is that I want to add products from cookie to a Wishlist ONLY if it is a new registered customer.

Not sure how to get newly registered customer wishlist?

Here is my observer ($list is array of product Ids, from a cookie named ‘guestwishlist’:

namespace VendorGuestWishlistObserver;
use MagentoFrameworkEventObserverInterface;
use MagentoFrameworkAppRequestInterface;
use MagentoWishlistModelWishlistFactory;

class CreateAccount implements ObserverInterface
{
    /**
     * @var MagentoCatalogApiProductRepositoryInterface
     */
    protected $productRepository;

    /** @var WishlistFactory */
    protected $wishlistFactory;

    protected $_helper;

    public function __construct(
        WishlistFactory $wishlistFactory,
        VendorGuestWishlistHelperData $helper,
        MagentoCatalogApiProductRepositoryInterface $productRepository
    ) {
        $this->wishlistFactory = $wishlistFactory;
        $this->_helper = $helper;
        $this->productRepository = $productRepository;
    }

    public function execute(MagentoFrameworkEventObserver $observer)
    {
        $customer = $observer->getEvent()->getData('customer');
        $customerId = $customer->getId();

        $list = $this->_helper->getGuestWishlist();

        if(isset($list)){

            foreach ($list as $productId){

                $product = $this->productRepository->getById($productId);

                $wishlist = $this->wishlistFactory->create()->loadByCustomerId($customerId);
                $wishlist->addNewItem($productId);
                $wishlist->save();

            }
        }
    }
}

Error that shows is ‘We can’t specify a wish list.’ when I observe event ‘customer_login’