Why some dots on the history map are not showing? Are they missing from the map?

History dots are drawn on the map in the reverse time order. Records with the same latitude/longitude are drawn on the same spot and overlapped with each other. In such cases, only the top one is viewable because it's drawn later. Others are blocked by the top dot, and you would see the dot numbers jumping. So the "missing" dots are still on the map. Only they are blocked by other dots.