Being that "Certified Angus Beef" is a brand name and a registered trademark (and we have been told about these), I would think that standard for Certified Angus Beef� are set by the CAB people and not the USDA. A quick look at their website explains the standards:
What is Certified Angus Beef � (CAB) product?
The Certified Angus Beef � brand is reserved for Angus beef that, after meeting the live specification of being at least 51% black-hided or AngusSource� enrolled, is verified by the U.S. Department of Agriculture (USDA) as meeting the ten CAB carcass specifications:
-Modest or higher marbling
-Medium or fine marbling texture
-"A" maturity for each, lean and skeletal characteristics
-10 to 16 square inch ribeye area
-Less than 1,000 pound hot carcass weight
-Less than 1 inch fat thickness
-Superior muscling (eliminates dairy influence)
-Practically free of capillary rupture
-No dark cutters
-No neck hump exceeding 2 inches