The D00 stamp is the assembly number and if all parts are original to the gun, you will find the D00 stamped elsewhere - frame, barrel, cyl, hammer, etc. The serial number will also be stamped on th backside of the right grip, if the grips are original. The rarest of all the Model Ones, 1st, 2nd and 3rd issues is the transition model between the round frame 1st issue and the flat frame 2nd issues. Serial numbers of these are in the low 11,000 range, mixed in with the serials of the last 1st issues, 6th variety. perhaps 25-40 of these transitionals were produced. Few are known to collectors. The side plates are 1/2 kidney shaped but with a 90 degree angle at the top of the frame cut. Ed.