The small photo that our AZ friend posted from the 21 food.com site sure looks like what I get as a ‘Trimming piece’ when the butcher ‘squares’ a rack of ordinary Spare Ribs for me. Sometimes called the Cap or Chin Bone(s) they link the ribs together.
Am I close?
Funny I have Never hear the descriptor ‘Bone-In’ used with a Beef Brisket !