It is written in the car manual that the fuel tank capacity is 60l (15.85 gallons I think).

But at my last fuel fill, I put 68 liters (18 gallons)

I have already experienced some 'overfillings' with my previous cars, and because of all the piping and my taste of risk , I already put 3 to 4 liters more than said in the manual.

But never 8l. Did you experience the same thing on your car?

Another thing, I have been told by my carseller that when the last square for the fuel disappears, rush to the nearest gas station as you have less than 10kms of fuel in your car.

Is it the same in your car (last square disappearing means just fumes in the tank)?