How good they hatch has everything to do with how they got from point A to B with almost any eggs. Some are more durable than others, for instance pheasant eggs don't ship well at all. Xray machines are hard on embryos (don't let anyone write 'do not xray' or its a guarantee they will), so are the constant temp fluctuations and the fact that they are surrounded by paper dessicating the air (too little humidity left after the paper sucks it up) The postal workers tossing them around breaks the air sac on a lot of eggs that don't look broken on the outside. Order as close to home as possible and explain to your post man whats coming (leave them a note if you have to, I think they can read but i've had more than one upside down box in my yard that says fragile so who knows).
Basically no two pieces of mail take the same route and the factors along the way are what screws up hatch assuming the fertility was good to begin with.