I have noted this before with ID's at bars. When you check an ID, you are assumed to be an expert in identification. People pay fines and are shut down for mistakes. You are assumed to be the authority on verifying documents by the liquor board. If you've ever been in court, the party (plaintiff or defendant) will hire a documents expert to give expert testimony as to the authenticity of documents. They are paid well to do this. I think that having a FFL verify a DC letter, is just setting them up for failure, like where the bar allows a patron to purchase an adult beverage with a "fake" ID. FFLs should not be authenticating State documents.