It's very common for hatcheries to mix them up. McMurray even says up front they deliberately mix them up for a "varied color flock".
So yeah.. hatchery stock are in a way like Easter Eggers. Nice heavy and productive birds(which is really more their goal- more eggs to set, more chicks to...
NN is basically semi-dominant. Which means a NN x not NN cross will throw NN chicks.
It's semi-dominant because there is a little bit of visual difference between birds pure and not pure for NN. Not pure have a huge bowtie with feathers covering either all or most of the lower front neck and...