GDC is probably what OP meant, as GDC was the UC Davis Genetic Disease Control.
The numbers still are in the OFA database, as the databases were merged. I understood that the hip x-ray procedures were similar, but that what was different was the exchange or sharing on an open database. They also pioneered elbow and hock clearances, to my knowledge. That being said, the evaluations may have been different or more stringent. I'd love to know more, but it would be knowledge most useful if using frozen semen.
Fron OFA's FAQ page:

"What do OFA numbers beginning with GDC mean?
GDC stands for the Institute of Genetic Disease Control. GDC formerly maintained canine health databases similar to those of the OFA. In the Fall of 2002, the GDC databases were merged with the OFA. Numbers beginning with GDC indicate that the evaluation was performed by GDC prior to the merge.?