"Palming Off"

P Knife Manufacturing Company v. D Knife Manufacturing Company for D's alleged unfair methods of competition in "palming off" a knife made by D to look like P's knife. Ddenies generally. At trial, P offers a letter it received from the National Business Gifts Company, a jobber of pocket knives, which states, "We did not find this knife in the catalogue but are sure you made it." The enclosed knife was manufactured by D. Admissible?