I love the fact that you highlighted this... I purposely refused stressing on this point since the post was already too long.
Now, like you said, indeed there are traces of sperm in precum. The only time these sperms are able to fertilize the egg is in a situation where an individual is done with the first round of sex and maybe after a while is aroused again.
At that point the sperms are potent enough since the urethra was already cleared of its acidity content (urine) before the first round of sex. However, if the person urinates before the second round of sex, I don't think the sperms in the pre-ejaculate will be able to survive. But well, I might be wrong. I'll have to read more on this. Thanks for stopping by. I really appreciate.