Tommy
I'm glad to hear that this is not a flight safety issue. (At least it is not a flight safety issue THIS time.) You still must report this, just because of the type of work that your company does!
I have some more suggestions.
A better way to legally prove that you did not back date the letter is to send it to your boss Registered Mail. Send a copy to yourself, (also by Registered Mail) with a copy of the postal receipt from the letter you send your boss. Do not open the copy you send to yourself. Place it in another larger envelope and mark the outside of it, and mail it to yourself again!
A picture with the day's paper in it only proves that you wrote the letter after the paper was published. You could have had that newspaper laying around for weeks, then wrote the letter and took a picture of it next to the letter.
There may be nothing come of it. I was on an inspection job, where the shop foreman forged my Associates signature on a follower sheet on a New York State Bridge Girder fabrication. We wrote up an NCR and mailed a complaint to the DOT immediately. There are Federal Funds involved in most State Bridges, and we were hoping something would be done to remove that particular foreman, but It turns out that the follower was for internal use only, so unless they filed the follower, no crime was committed.
However, I have seen this type of thing blow up before. I had a consulting job that I couldn't handle, so I referred it to a P. E. friend, who was an expert in that type of welding. (I don't know if you are old enough to remember the ABSCAM Scandal and the WEDTECH Scandal.) Almost a year after that referral, my friend was raided, right after daybreak, in the middle of the winter, by the FBI. They hustled him and his wife out of the house in their night clothes to wait, while they searched the house and took all his computer equipment. They blocked the whole street and the neighbors couldn't get out to go to work, until the FBI finished searching the house. The neighbors must have thought he was a major drug dealer!
It turns out that WEDTECH was a major defense contractor that was getting kick backs from vendors and had a bunch of phony "Consultants" that they were charging to the government. Anyone who was listed as a Vendor or as a Consultant for WEDTECH was raided and investigated. (I never responded to the solicitation, so I was not listed.) My friend registered with them, but never did a dime's worth of work for them. He only got his computer back a year later, and nothing worked right on it and all of his personal data was scrambled or lost.
Do not agree to keep this secret, after your boss is told. You can agree not to discuss it with anyone but the proper authorities. Do not participate in any discussions where the company decides to keep this quiet or slants the information to minimize damage to the company. It is all too easy for you to get involved in criminal "Conspiracy". Smart, well intentioned Lawyers get caught up in "Conspiracy" crime, and do not even realize it, until they are arrested. Do not tell the newspapers or the rest of the world. Let your boss and the company attorneys handle it, but do not even agree to get coaching from the company attorneys on how to present your answers to investigators, should this issue come that far. They can steer you into conspiracy actions, and remain blameless. It is you who would commit the actual crime.
I hope all turns out well. CYA
Joe Kane