There are many instances where a legal gun carrier stopped a crime that do not get reported mostly because there is nothing really to report, a crime was not committed.
I carry. Once several years ago while I was fixing a computer at church and was the last person there just before dark as I left the building I saw a man testing all the windows to see if one were unlocked. He was an unkept man with a long beard and I assumed he was up to no good. I confronted and told him to go away. He acted like he was deaf. No matter what I did to try to communicate with him as I told him to leave he kept throwing up his hands like he couldn’t understand me. I pulled back my suit jacked and showed him the hilt of my gun in my trousers and his eyes got very big and suddenly turned around and quickly left the property.
What could I have reported and what news agency would have found it worthy of a story? Nobody would be interested in it. Regardless it was a gun incident in my opinion. I have never had to shoot my gun at someone and I hope I never have to but it has likely stopped at least one crime simply by being there.
Lott has done some good longer articles / papers putting some national estimates on that sort of thing.
The value of a gun is the deterrent value like in your story. Most people don’t report them out of fear of becoming the criminal for brandishing one.