It should have the true SN on the bottom of the grip frame, and in the frame yoke recess (under the barrel with the cylinder out, under MOD 27-2). Any other numbers are probably factory internal codes.
They would be in the N60000 range, plus or minus. The serial number would be the one off the butt of the grip frame. You are probably looking at a five digit assembly number on the yoke,
The serial number (beginning with an N) is stamped in the yoke cut along with the model number and on the butt. The assembly number is stamped on the yoke and on the lower left hand corner of the the grip frame.