Notice that the voltage axis starts at $$\1.2V\$$, and over the typical operating range of the diode, the voltage only varies about $$\0.6V\$$. This is mostly due to the internal resistance of the diode, which in this case is about $$\13\Omega\$$. If you are going to put this diode in series with a $$\4.7k\Omega \pm 1\%\$$ resistor, then the $$\13\Omega\$$ resistance of the LED is quite insignificant compared to resistor you've added, which might deviate $$\\pm47\Omega\$$ from the nominal value of $$\4700\Omega\$$. Put another way, that $$\13\Omega\$$ of resistance from the LED represents a $$\0.28\%\$$ error in your calculations.