You may want to check the values you are using for analog in.
If you assume a reference of 5V, and 1024 possible analog values, then you get:
value= 1024 * voltage / 5
If you allow around a +/-200mV from those points you get the following value ranges for your if statements:
2V = 408 -----> 368 to 451
3V = 614 -----> 573 to 656
4V = 819 -----> 778 to 860