I find this varies a lot with not only the breed, but individual birds and the lines within the breed. For example, we have a silkie hen that lays medium sized eggs that are significantly larger than some of my friend's silkie eggs. We also have a lot of Cochins that are laying 5-6 eggs a week their first year (and about 5 eggs a week in season 2), which is more than that breed is purported to lay. We don't use artificial light, which is also a major factor in boosting egg production in some breeds. It's hard to know where the hatcheries get their information from if they don't reference it