A factory letter written by Roy Jinks will provide an overall history of the model being lettered and is standard for all letters issued. The specifics about your particular gun (i.e. shipping date, barrel length/finish, date shipped and location, etc.) are stored in various locations (some records held by Roy, some by S&W) and the factory invoices for many guns are located at the Connecticut Valley Historical Museum in Springfield, MA. Once Roy determines the shipping date and location shipped (by serial number), he asks the staff at CVHM to manually pull the invoice and check the features of the gun and verify the shipping location. That is how the barrel length, finish, etc. are verified (or it is determined the gun is not original). When CVHM gets back to him, Roy completes the factory letter on his computer.
Guns made after computers were in use have records with much less information about features (so I am told) and Roy has to travel to Springfield to get what data there are.
All of this takes time and the $50 fee is still a bargain in my opinion.
In time, it is a goal of the Smith & Wesson Historical Foundation to digitize the shipping records and the factory invoices. This may result in a more streamlined process, but will require a lot of time and money to complete. That is why all collectors should consider supporting the SWHF.
Bill