Try 1908, Siberia.
Consider that two-thirds of the surface is ocean, which would mean the only evidence of such a hitg would be tidal waves. We might have no knowledge of the Siberian hit except for a few curious scientists. It wasn't even suspected of being a meteorite or comet until the 1950s.
Hey, wait a minute. I live near a coastline!!
The midnight sky in London was bright enough to read the newspaper after the Tunguska event.