After about serial 2400, the marking was put on the top of the barrels in two lines.
About serial 1600, an extractor was installed on the left side, between the barrels. There are a few DDs with the marking, 'Remington's Ilion NY USA' but there is no known reason for this marking. ) After the first 100, the 'manufactured by' was no longer stamped between the barrels. Patent 51,440, 'Improvement in Many-Barreled Fire-Arms', which describes the key features of the original design in some detail. (This refers to firearms inventor William H. 12, 1865' stamped on the left side of the barrel. REMINGTON & SONS, ILION, N.Y.' stamped on the right side of the barrel and 'ELLIOT'S PATENT DEC. The first 100 Double Derringers have 'Manufactured by E. Production prior to 1869 had no extractors.
The Remington Double Derringer was made from 1866 to 1935.