Having a boxed gun is great but not definitive. If it's something special of a gun a letter only helps confirm it. As everyone knows a lot of fakery going on with boxes and labels these days. Just look on EBAY. If it's a standard model with a age correct box and what appears to be a legit label a letter may not be worth the extra expense. It really boils down to what you have or think you have and what you may need to verify it.