Meat cut definitions have changed. Forty years ago, my father, the butcher, would have insisted that only two Porterhouse steaks can be cut from a side of beef. He preached that the remaining steaks cut from the short loin are T-Bones, no matter how thick they’re cut. Today’s butchers rename a T-Bone to Porterhouse if it’s more than 1¼†thick.
Correct me if I'm wrong, but I thought the USDA naming difference between a T-Bone and a Porterhouse is based on the "width" of the filet portion --- not the thickness of the steak.
Definition: "According to the U.S. Department of Agriculture, combo steaks cut from the short loin that contain a tenderloin section that is at least
1.25 inches across at its widest point qualifies the steak as a Porterhouse. A filet portion with a 'maximum width' between 1.24 inches and 0.51 inches makes the steak a T-bone instead. A filet portion less than 0.5 inches at it's widest point is simply a bone-in strip steak."
If you really want to impress your butcher, order the steaks by their IMPS (Institutional Meat Purchase Specification) numbers: 1174 is a T-bone; 1173 is a porterhouse. Then there should be no mistake.