Hello! To add to your blog-posts, here is one by our veterinary team: https://vethelpdirect.com/vetblog/2022/07/13/when-do-a-dogs-balls-drop/
and another (quite old now) about cryptorchidism: https://vethelpdirect.com/vetblog/2013/11/26/ask-a-vet-online-my-dog-only-has-one-testicle-down-what-is-the-best-age-to-have-him-neutered/
If testicles remain in the abdomen (often tucked away by the kidney), they will be at the wrong temperature to develop (dogs' testicles develop in the scrotal sacs, which are much cooler than the abdomen). The hot abdominal environment can result in a remarkably high rate of testicular cancer in the developing testicle, but of course this is difficult to observe / feel when it's hidden away up there. This unfortunately means that there are many cases where testicular cancer takes a dogs' owners by surprise.
So, although cryptorchid dogs are usually infertile, castration is strongly reccomended in these individuals. Vets seem to vary slightly in when they recommend this but as your dog is over a year of age and likely to have reached his adult size, it sounds to be time to visit your vet.