Well, I'm no expert here since I'm incubating my first clutch...but even candling that one clutch I found tremendous variation within the veins. Some were strong and robust...another egg I was less certain about because it just had veins on the very, very top of it and none down the sides. I could barely see anything in there.

They are all doing well 40 days later though.

Maybe it's just totally random??

JonV