Board Thread:The Panopticon/@comment-1293767-20151029072618/@comment-26469787-20151030041147

Yes, as co-writer credit, especially in the case of the showrunner, should not be able "contradict" the fact that the writer has written both parts of the story. If, for some exceptional reason, a writer chose to write one part of their story with a partner, and another on their own, it is still extremely likely that it could be classified as a two part story. But in your hypothetical, as in the upcoming Zygon two-parter, the fact that an episode has been "co-written" with the showrunner, a person with great creative influence over the final script regardless, should not discount that it is one writer's story, and they therefore have created a cohesive whole.