confused

I attended a gun show Saturday and a young fellow was walking around trying to sell his Colt 2nd gen SAA. It was pretty obvious even to myself a novice on SAA guns even if I have 5 of them that this gun had been pieced together, the bluing on the barrel was about 90 % and the gripframe /backstrap bluing was somewhere in the 65 % category with extreme handling wear. the side screws showed evidence of remove and the 3 numbers on the loading gate didn't match the serial of the gun, also it appeared the ejector shroud had been removed. Needless to say I passed on the gun even at 1200 bucks. Where Im confused is the 3 numbers on the loading gate verses the serial number of the gun. Do these numbers always match up,on the 5 guns I have they do, but they are all 3rd gen guns. A friend told me that the 3 numbers on the loading gate and last 3 numbers of the gun serial number should match on 1st and 3rd gen guns, but 2nd gen guns were different in the 3 numbers on the gate were assy numbers and only matched the number on the right side under the grips. Id appreciate any and all thoughts on this, Thanks Smoke