Because some types of arthritis are often progressive, prior radiographic imaging - such as X-ray, MRI, CT - may not have detected the extent and can only do so if there is progression.

DJD, DDD, degenerative arthritis all mean the same: Osteoarthritis (OA).

Do you have the radiology report from 11/06? If so, I'd take a copy of that along with the most recent report to the doc. whom ordered the latest films and ask the doctor about the findings from both.