>>but it is only ever prime rib if the grade is prime, if not, it is standing rib roast.
I do believe the USDA label regs specifically provide that a chunk of meat labeled "Prime Rib" is a name of a cut and when so labeled/identified is not required to be of USDA Grade Prime.
local habits / butchers / terms may vary.
/quote USDA pub
(N
NOTE: Prime rib is not named for the quality grade “USDA Prime.”) The ribeye muscle (the center muscle) provides structural support, rather than
mobility, and is therefore quite tender. It also contains large amounts of marbling compared to the rest of the carcass and produces rich, full-flavored roasts and steaks. Although roasting the ribeye muscle on the rib bones produces a moister roast, the bones can be removed to produce a boneless ribeye roast. Ribs are meaty, flavorful bones separated from the ribeye meat and are often served as barbecued beef ribs. Rib meat