Elliot, here's the thing. 1951 was Singer's 100 year anniversary. Singer also had excellent marketing techniques. There is nothing special about the machines built in 1951, unless they have the Centennial badge. Singer also provided additional badges to their dealers, who could replace the gold badges on their older stock. Centennial badges have been found on machines produced as early as 1949.
A black 301 is the favorite of the 301s to have, because of the color, as black was not used as much as the tan. A black 301, Centennial badged, in very good condition, with all original accessories, and in a good trappy #74 cabinet is a pretty nice set.