I also have had the experience of having to have a dog re-x-rayed under a second anaesthetic. I am firmly of the opinion that the laying out for HD x-ray is a specialist job. I will require an x-ray for my pup in about 7/8 months time and will be asking around for an experienced vet regardless of my close association with my own one, particularly with his help with Freckles.
As to the panels, I do not believe there is that much variation. These people are also very experienced, and fully qualified, but there are so many plates to look at that they do not have long to examine each one, so the plate MUST be first class, and the dog laid correctly.