[Mrs. Robinson]

Originally Posted by CFrance

You seem very knowledgeable about this, slipcovers. Back a few decades ago, Prime rib roast was a standing rib roast of a prime cut of meat. In a restaurant, a slab of meat called prime rib was cut from that. I think somewhere along the line people started referring to the roast or slab as prime rib even if it wasn't a prime grade.

Am I anywhere near correct?

You are very correct!

Some decades ago, and I don't recall how long it's been, what was called choice then, has become prime now.
And while prime rib can be very tender, it is not one of the cuts of meat that is known to be "prime" by definition.