Question about debunking a local legend with a county plat map from 1961

There's this story around my town in Ohio that a tunnel runs under the old courthouse, and folks swear the city covered it up back in the 60s. I got tired of arguing about it at the diner on Route 4, so I pulled the county plat maps from 1961 at the library annex and found a storm drain line that matches the "tunnel" path almost perfect. Then I grabbed a cheap endoscope off Amazon for $32 and poked it into the grate behind the fire station, and it's just a brick culvert full of leaves. Now I don't know what to do with this, because half the people I show the map to say the real records got swapped, so how do you all handle it when you actually dig up the paperwork on a local legend and it just makes people dig in harder?