Possible chess positon after X ply? I've started to code my own little engine recently and am now working on a perft function which simply sees how many moves there are.
Trying to get correct results I searched online for the correct amount of possible positions after e.g. 4 moves.
Now according to these sources: 

https://youtu.be/6Y_FaQhqX2c?t=5m46s

It should be 197281 possible positions after 4 moves, and I can reach that in my code!

But switching a bit around in my code to get some optimization which seemingly shouldn't change anything, I get a different number: 197742
Now I would think that is wrong but I have found different sources again, claiming that is in fact correct:

https://youtu.be/Km024eldY1A?t=5m33s

So, which one is it? 197742 or 197281 possible positions after 4 moves?
I was a bit uncertain whether this belongs here or on StackOverflow.
I went with this one, I hope that's alright.

EDIT: apparently I can't post more than two links due to my low reputation
I'll post the links in comments

Thanks in advance
Folling
The chess programming wiki is correct:


  https://chessprogramming.wikispaces.com/Perft+Results


197281 is the number. I remember I used Stockfish to generate the same number while debugging my code.