Generally speaking, factory letters will provide specific details about the firearm as it was shipped (caliber, finish, barrel length, optional features), when the piece was shipped, and to whom (dealer, distributor, etc) it was delivered. This information serves to confirm authenticity (assuming it remains as manufactured) and establishes a base point for documenting provenance.

This is not an appraisal or opinion about present condition or market value.

Again generally speaking, commemorative issues may tend to have lower market values than comparable standard production pieces, the exceptions being those purchasers desiring that specific commemorative for personal reasons or to complete a collection within a series.

In the case of the OP's revolver the persons likely to be most interested would be those with a close personal connection to NCHP, or perhaps a collector who limits his acquisitions to commemorative issues.