I did had a bitch on breeding terms, I let one go on the understanding I would get a puppy back when she was mated, but like you, it never happened, in fact they sold the bitch.
I do ask the pet people to send me photographs which is not ideal but gives my an idea of what they look like, I never ask them to bring them back.
I find when you sell a puppy the owners are not keen for them to have a litter, I did ask to use a Welsh I sold once who was ideal, and took my bitch to the dog, but like most dogs not use to this situation got himself into a right state, I went back two days later but he was no better so I failed to mate the bitch
That was the first time I ever failed mating a Welsh, so I am not over keen to waste time using an inexperienced dog.