Guess you want explanation on natural family planning (coitus/withdrawal method) as you sited above, well, if a guy is able to pull out and ejaculate outside during the first round and he is able to do the same irrespective of the number of times, then there should be no pregnancy at all unless there is a drop inside as a result of imperfection of men.
Hope I got your question and you are satisfy else I will like to know more of what you intended.
Thanks