Both the K-frame and L-frame are clearly medium framed guns, though one is larger than the other. So calling one of them a large is wrong.
Also, both the K and N frames existed long before the L frame. Important because those would be medium and large frames (the J-frame was around before also). Then another medium frame was offered. This doesn't make the N-frame extra large, but it becomes small, medium, medium, large.
Plus, the X-Frame is clearly the extra-large frame.