Be careful about discussing this. A lot of breeders have been using a two week rule for a lot of years and do not want to think about the idea that they may have ad mixed up breeding.
The problem with the theory that the new pushes out the old is that there is not pressure involved in chicken breeding. It is not like other animals. The Rooster has not appendage. It is a splash and take kind of thing LOL.
Make sure that the breeder you get hatching eggs has not waited only a week LOL. Something to watch out for since, to me, it is deceitful to sell them knowing there may not have been enough time to make sure the old Rooster has cleared.