This is what AFCCO says chicken by-product meal can contain:
Chicken By-Product Meal: consists of the ground, rendered, clean parts of the carcass of slaughtered chicken, such as necks, feet, undeveloped eggs and intestines, exclusive of feathers, except in such amounts as might occur unavoidable in good processing practice.
You can find all the AFCCO definitions here:
Pet Food Ingredient Definitions: All Critters ~ Pawprints and Purrs, Inc.