Accuracy of HD & ED x-rays at 6 months?

Not accurate enough to know for certain if the dog will pass certification as an adult, be breed worthy, etc... But any dysplasia severe enough to have a significant impact on the dog's future quality of life or ability to work is likely to be evidant at 6 months old.

And knowing there's a problem earlier gives you more surgical options if you go that route.

Knowing if there is a problem before you buy the dog makes your decision easier. I personally would not buy a dog if the prelimes showed a problem. Also things can change as they get older even with the prelims showing no problem.

Here is a link to OFA and their findings on accuracy of Hip Prelims.
http://www.offa.org/hipprelim.html

I don't think Elbow Prelims are as good as Hip Prelims.
http://www.offa.org/elbowgrade.html

Would I bet the farm on a good prelim passing at 2 years old, no but at least I know there is a better chance.

The OFA stats seem promising about it. Even though the breeder has some guarantee about hips there is no way I could give back a pet i've bonded and spent countless hours with.