A very good question, and one I can only guess at. I am sure SOMEONE has attempted a careful photographic comparison, but the problem is that any impact big enough to leave a crater more than a hundred meters across, would have been a spectacular impact that no one would have missed. Impacts of just about any size kick up so much rock and dust that even an impact that leaves behind a crater too small to be easily seen in a survey photograph, would produce a collateral plume of rock and dust, and a flash of light from incandescent material, that I suspect would be detectable. There have been numerous optical flashes seen on the Moon over the decades. These seem to be real enough, however, its is not known whether these are from outgassing or from impacts.