My guess based on a similar situation with S&W is that the OP's friend is not the original owner of the 640 and bought it without any paperwork being filed, (I can't think of the form number, but it's the one that goes for the background check. )
Otherwise, S&W would have replaced the gun with a new 640 if they couldn't repair it. I had a 640-1 that I sent in a couple of years back that was deemed unrepairable. I purchased the gun at a pawn shop and filled out the form. The gun was replaced with a new 640-3.
Consequently, a close friend gave me a 637-2 before he passed away. No form, so no record. The 637 developed a problem and I sent it in to the factory and received a similar letter. No replacement was ever offered.
The form is used by S&W to track guns for warranty purposes I believe. I have no proof of this other than my experience, but I do realize that if I buy a gun from a friend or relative that the warranty isn't available to me.