You only know that the cold caused your result if you repeat it three or four times with the same result.
You'd only know that Washing... which you also did, caused your result if that's all you did and you had the same result three or four times.
You can't know from a "first" experiment what your results would be for the 2, 3, 4 or 5th time.
You know that hatch of that group went poorly. Same parents? Same age? As your "test group" if not then not at all the same from the beginning.
Experimentation is only as good as your controls. You had at least two variables - washed and refridgerated. If they were also a different breed, even different parents, add more variables. Were they at one end of the bator or the other? Do you know for a fact temps are even on both sides of your bator? Mine aren't.
You know they did develop. You don't know that it was the first two variables that meant they didn't successfully hatch.
Did you have temp or humidity swings?
You actually probably had too many variables for a first try to draw any meaningful conclusion. I include refridgerated and cold eggs in every hatch, from the same few birds. While it does slightly decrease the hatch rate it's no more damaging than something like shipping.
I'm toying with turning the refridgerated eggs more to see if that improves hatch rate.
That's next. I don't wash eggs.
Each thing you do differently matters. Each difference in what kind of egg, parentage, age - all matters if you're trying to compare something.
Notes help. You have to know what spiked, or fell, how many times you did turn. What your humidity was and whether it did swing too much in the end. Or with ducks, too little.
Once isn't enough to draw a conclusion. If you really want to know you do it several times with notes.