Emphasis mine obviously, but I think (and hopefully you agree) that's a minimum. And that number is birds to select from for yourself. If you hatch 100 and sell 75 of them and only raise out 25, that doesn't cut it either if you want to make progress. The more you hatch the faster progress you'll make that year too.
Matt, all I can comment on is my own experience. Last year we did put roughly 100 chicks on the ground, for each breed, roughly 200 chicks total. From the very beginning, we culled those who were "not right" or injured or deformed. Then, as time goes along, you cull those which are obviously not what you're looking for. The numbers keep dwindling. Great meals are eaten!!
The layer flock begins fill for first year pullet layers (non breeders). A good thing come next winter.
As summer draws to a close, we may be down to maybe 20 birds of the original hatches. By Halloween, that's it. The winds are blowing colder and winter is surely coming, once again. We make our final commitments to maybe, maybe 3 or 4 pullets and those 3 cockerels. Three cockerels, not because we're thrilled about all three, but the Peter Principle of "sure as heck, one will die, one will get killed or whatever" and we really just want ONE to make it to spring. As the three pullets winter over and dagnab it, one of them will mature with a poor looking cushion or something. Sigh. Stuff happens.
Suddenly, those 100 chicks from last spring are reduced to just 2 or perhaps 3 birds, plus the 4 or 5 older adults and off you go, on another year of making matchups. That's it. Just my experience, for what it's worth, which isn't much. Folks can glean what they want and just leave the rest.