Goldsman brings up the classic TOS episode “The City on the Edge of Forever” as the ultimate example of not only a great episode of Trek but also how it’s demonstrative of the limits of the classic series. We got to know the TOS cast fairly well from 1966 to 1969, but it’s not like the characters had complete arcs.

You'd think the show itself would clarify who the mysterious bartender glimpsed in 'Wedding Bell Blues' actually is, but instead you'll have to read an interview to know for sure.