Yes, exhibition breeders will hatch 100+ a year to get the most perfect birds. But people will hatch based on what they can accommodate, which for me was about 30-50 of each of my two breeds. Yes, it may take more than a year to pick your breeders. But selection starts at day one.
Everything has an age where you can cull at. I’m going to use non breed specific examples, so it includes, but is not limited to:
Some problems are noticeable at hatch like birth defects.
Others like slow development can be noticed a month or so later. After about four months, you can make your first selections based on type, size, and comb, but only bantams and only outstandingly poor ones. At the age of five months you can do this with large fowl.
At 6 months you finally can pick your best group and maybe sell the others and at eight months you can finally pick the ones you will use for breeding with confidence. They don’t do much growing after eight months, but they will fill out more. Certain varieties such as laced, quail, and black tailed red may need a year before you can determine if the hens are worth breeding from but cockerels of eight months are generally considered breedable.