The Germans actually recorded different targets from the RAF's intentions on several occasions.
Flying round in the dark without GPS, or even any inertial systems, hardly bears thinking about. Half the time you probably wouldn't even have the stars...
Airspeed, which way you're pointing, what time it is and a good guess at what the wind might be doing where you were, was the basis of where you might be at the time.
Now and then you might see a bit of a river, or something else that might be recognisable.
Once you started evasive tactics, you could easily drift off to one side, unless you kept a careful count of what was going on.
Things got better with the various 'beam' systems, but you could still get confused...
I once got lost, on foot, in daylight, in the fog, in a field that I (thought I) had a reasonable knowledge of...