Besides the date and destination of the shipping of a S&W, the factory history letter also normally states the features the gun had originally, such as the barrel length, finish, stocks and any other optional features like cartridge chambering, target hammer and/or trigger or sight blades. For a "shooter" gun, none of this may matter, but for buyers and sellers, a gun with unusual features can be worth quite a bit more if it can be shown to be original. For example, a factory nickel finish on a K-22 is very rare if it first shipped with it. An early .44 Magnum first shipped with a 5 inch barrel may be worth twice or more what the same gun with a 6-1/2 inch barrel would be. Guns manufactured more than 50 years ago can be classified as "curios and relics" by BATFE, which allows those with C&R 'collector' FFL's to have the gun shipped directly to their premises, without having to go through a commercial FFL holder, which will often save some bucks. This information can be valuable for many guns, well worth the $50 cost of the letter.
Other times, it is just interesting.
Enjoy your K-22. A good .22 revolver is one of the most fun guns we can have.