Some years back I purchased a W & C Scott Pinfire 12ga. It did not have a SN, but did have the customer's name for whom it was built engraved on the rib. A letter to Mr Crawford revealed it to have been made ca 1863-65 under Matthews Patent. He also noted it eas the first "Breechloading" Scott he had reference to which was not SN'd.

He did not specifically say so but it sounded as if he would not have been suprised for it not to have a number had it been a muzzle loader.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra