The reasoning I heard about inserting the recipients FFL in the box, was in case the shipping box is damaged and the address label is damaged and/or unreadable. After seeing the conditions of some of the boxes I've received goods in the mail, UPS, and Fedex, I think this is a wise precaution.
Bob
Sorry Bob, bad answer...
First, BATFE says you, as a non-FFL, should not have the copy of the FFL to start with.
Second, an address inside is a fine idea, no need for it to be a piece of paper you are not supposed to have.
Third, it perpetuates the myth in some folks' eyes that they should get a copy they do not need, turning them into whiney little bitches.