Serial numbers on the military and commercial models were stamped on the butt in two lines, with military models having US Army or US Navy stamps on the butt and military inspection stamps on the frame.
Other parts of the guns were stamped with factory assembly numbers. These numbers were stamped on parts during manufacture to keep fitted parts together until an actual serial number was assigned and stamped on the butt.
These assembly numbers are not serial numbers and had no further meaning once the serial number was stamped.
It's not unusual to see New Army & Navy revolvers with the serial number and military stamps removed from the bottom of the butt, and people assume the assembly numbers are the serial number, which they are not.
It's also common for owners to refuse to accept that the butt stamps were removed without leaving any signs of removal.
Because it was easy to remove stamps from the flat bottom of the frame, Colt began stamping double action revolvers serial number on the frame under the barrel where the cylinder crane seats, on the crane itself, and often inside the side plate.