Some months ago, while searching for information on possible family portraits, I stumbled across this book, Catalogue of the Revolutionary Relics Exhibited at No. 56, Beacon Street, June 1875, in the Internet Archive noting the existence of portraits of my 5th great-grandparents, William Greenleaf (1725-1803) and Mary Brown Greenleaf (1728-1807). [see p. 5.]
I noticed a couple of interesting things in the entries (no. 43 and 44) on page 5, listing the Greenleaf portraits. In this scan from the University of Michigan original, someone scratched out the artist name "Copley" and wrote in "Blackburn". I wondered if this was simply a typo, or if the portraits were ever actually attributed to Copley.
The second interesting point is the notation under Mary Brown Greenleaf's portrait regarding piercing by a British bayonet. I presume that to mean there is at least one hole in the canvas. How it got there is anyone's guess, but given that the family came from Boston, I suppose there could have been a British bayonet in its vicinity at some point.
Further searching turned up this book in the Google Books collection, Metropolitan Museum of Art Catalogue of Paintings, by Bryson Burroughs (6th ed., 1922). Entries for the William and Mary Brown Greenleaf portraits on page 18 indicate both that the portraits are signed by Blackburn (not Copley) and attribute the holes to "bullet holes, which according to tradition were made during the Revolutionary War."
I found copies of the portraits in the book, Early American Costume, by Edward Warwick and Henry C. Pitz. But the black and white plates don't show enough detail to tell me if there are bullet holes. Both the William Greenleaf portrait (plate XXVIII-A, facing p. 129) and Mary Brown Greenleaf portrait (plate LI, facing p. 232) have specks that might be holes, but there's no way of knowing. I don't know where the portraits are today. This work also attributes the Greenleaf portraits to Blackburn.
It's probably safe to say that the works are by Blackburn, but there will likely never be a definitive answer about the bullet or bayonet holes. In any case, it still makes for a great story, made even better by finding it in print in a couple of places.
 Ladies' Centennial Commission (Boston, Mass.) Catalogue of the Revolutionary Relics Exhibited at No. 56, Beacon Street, June, 1875. Boston: Ladies' Centennial Commission, 1875. Online. Internet Archive. http://www.archive.org/details/cataloguerevolu00bosgoog : Accessed 4 July 2010.
 Burroughs, Bryson. Catalogue of Paintings. New York: Metropolitan Museum of Art, 1922. (6th ed.). Online. Google Books. http://books.google.com/books?id=TPAoAAAAYAAJ : Accessed 4 July 2010.
 Warwick, Edward, and Henry C. Pitz. Early American Costume. New York: The Century Co., 1929.