You cannot make that assumption at move 3. Even at a very low intermediate level of chess, you can easily know an opening like this for 8 - 10 moves across 2 -

You cannot make that assumption at move 3. Even at a very low intermediate level of chess, you can easily know an opening like this for 8 - 10 moves across 2 - 5 variations. I know cause I do. Master Level Prep of the Kings Indian goes 20 moves deep across 5 - 8 possible variations. This has been demonstrated over the board several times. It's trivial to find opening theory lessons on youtube on playing the kings indian defence covering 5+ counter lines going 10+ moves deep, even on weird lines. And then there are books about this opening. There is zero value in starting to cheat on move 1.