I understand it has to do with the marbling of the meat. Does the grading system apply to the entire cow, as in any cut from this cow is considered prime/choice/select? Or is it done by the portion of meat cut; could the same cow produce both prime meat and sub-select meat? And who came up with prime-choice-select instead of a simple letter grading system?
The grade is by whole carcass.
History of beef grading in the US