An interesting thing about grading--the information Andy passed on is valid only for USDA graded products, with that little shield/letter symbol.
States can have their own grading systems, they can use Grade A or whatever grade they choose, and their standards may be higher or lower than the USDA grading system.
A company could even call their products Grade A, and not have to meet any standards at all.
(I was a USDA poultry grader for mercifully brief period of time.)
I just haven't been the same
since that house fell on my sister.