Most gun manufacturers never did anything at an exact serial number. S&W is no exception. All the books say that the 5th model starts at #539001.
The front sight blade on my gun is forged to the barrel and NOT pinned. All the numbers on my gun match. I know, I checked before I bought it.
The grips are another story. I know on rubber and wood grips the serial number of the gun is either scratched, penciled or stamped onto one or both of the insides of the grips. But I don't know if they did that on special order grips, such as factory pearls or ivories. I've asked around at gun shows and no one, not even dealers, can seem to answer that question. One old dealer that I did talk to told me that sometimes on special orders they would ship the gun with the standard grips on them and include the special order grips in the box. You had to put them on yourself. I did take my grips off and check and there is nothing on the inside of either of them. If they were penciled, it could have easily been rubbed off during a cleaning if the grips were taken off.
Even if the grips aren't original to the gun, they still add value to it. They are, in fact, S&W factory pearl grips. And they compliment the nearly mint condition of the gun quite well.
All these reasons is why I am waiting for my factory letter. Might be a few months before I get it. What ever the outcome I will post it here!