Below is the link to a cohort study of 48 dogs and how HD progressed over time, and an indication of the predictive values of OFA screening versus PennHip
Chronology of Hip Dysplasia Development in a Cohort of 48 Labrador Retrievers Followed for Life - Smith - 2012 - Veterinary Surgery - Wiley Online Library
I may consider doing PennHip in future along with OFA.
On the plus side, at least diet, nutrition and exercise, seem to have an impact into progressive changes at the joints. This is good news for all pet owners of dogs with HD or even ED.