If all medical professional refuse to agree on how DDD happens maybe they should separate symptoms into different category's and here's my reasoning.
When an individual is hurt on the job or many years after injurying themself it is always easier for a examiner for the insurance company to state that person has DDD. If DDD is a natural aging process then let the medical profession call it DDD however, if a person is in the 20's, 30's 40's and usually good health who suddenly has an injury it related back to DDD and insurance companies refuse to pay because its a natural process.
It's easy for Workman's Compensation to find a doctor who will diagnose medical injury's to DDD leaving the employee out of a job and no insurance to cover thier medical cost.
Just because the sun comes up everyday doesn't mean its going to be Warm.