X-ray said 8 puppies, but only 7 born. Is another puppy coming?

If the radiographs were taken after 42 days gestation the puppies skeletons should have been calcified which means your vet should have been able to count heads and spines and give you a fairly accurate number of puppies. If they were taken before the skeletons had calcified it is much more difficult to get an accurate count. I have been surprised in the past when it turns out some of my patients have had more than the original guess from the radiographs. This can happen if two puppies are superimposed, or overlapped one on top of the other in the images, making it look like two puppies are just one. However, if your vet saw 8 skulls and spines and you only see 7 puppies my thought is there is still one that hasn't been born. If Sugar still doesn't give birth to that eighth puppy in the next few hours I would call your veterinarian. I hope this was helpful!