The Sterlingworth checkering was flat-topped all during the Philadelphia era, so your gun may well be just the way it left the factory. I did a two-part article on the Sterlingworths in The Double Gun Journal, Volume Fifteen, Issues 3 and 4. It may answer a lot of your questions. Also try the A.H. Fox Collectors Association web site --

http://www.foxcollectors.com/sterlingworth%20directory.htm