The way I rationalised it in my head, is the empire sent out a bunch of ships to look for the rebels, but the rebel base had a jammer up so the empire couldn't report back, and then the rebels had to kill every last one of them to make sure none of them could make it back off the planet to report back outside the jammer field.
If they pulled it off to the empire it would seem like one of their ships just went missing, presumably lost in an accident.
The massive kicker would be after two hours of solid fighting making sure the empire never finds the base, in flies the falcon with the tracker on board.
