The Caldwells of Castle Caldwell were baronets - Knights where the title was passed by heredity. One of the family tried mightily for years to be elevated to the peerage but was unsuccessful. I will look the story up and post it at a later date. The knighthood expired on the death of the last known member of the direct male line who was the governor of Lower Canada. But I will look up the facts and get these posted as well.
Cunningham does not pursue the descendents of the family far into North America and I personally believe that the family still exists through other lines. If so someone might have the right to call himself "Sir".