Back when I attended Virginia Tech, the meat that got delivered to the dining halls had the following message stamped on the outside of the boxes:
“USDA - Beef - Fit For Human Consumption”
Way back when during my college years, I worked a couple of summers at a packing house.
On the beef line, we usually saw 300 lb or so beef halves come swinging down the line. There were a few huge bulls that would come down almost dragging on the floor.
By watching the inspectors (my job was to help move the carcasses into the cold room immediately after the inspection station), I learned what is and isn't prime. It's pretty simple, but the fine scale marbling that is prime doesn't show up in the retail stores - nor is it apparent after the meat has been cooked. What you see in the best of the retail isn't really prime (using the 1970 standards), but a reasonable approximation to 1970 choice - which has been elevated to prime in the ensuing years.
But on a couple of occasions the carcasses were from milk cows - extremely skinny & bony & lightweight. I was told they were destined for the school lunch program. If so, it was a real rip-off, as the meat to bone ratio was miniscule. There seemde to be more tendon and gristle than muscle on those scrawny things. I think (but may be wrong) that the inspectors that checked the usual run of beef didn't have to bother with these.
“USDA - Beef - Fit For Human Consumption”
Now, that's really reassuring. :=)