Neil Simon is depicted as grieving the death of his wife of twenty years, Joan. While it is true that Simon was devastated by Joan's death, it is also true that three months and one week after Joan's death, Simon met actress Marsha Mason (on the first day of rehearsals for his new play, "The Good Doctor," in which Mason was starring) and they were married three weeks after meeting.
Ann Reinking was not just another showgirl that Fosse seduced. She became his protege and would go on to be a successful choreographer/director in her own right, ultimately creating the hit Broadway tribute review "Fosse."
After Paddy Chayefsky and Neil Simon are a bit taken aback by Zofia, the cook, Bob says, "Mike and Margot say she's the best cook on Long Island." The "Mike and Margot" Bob is referring to are director Mike Nichols and his then-wife, Margot Callas.
When Bob Fosse asks Paddy Chayefsky about his "TV news script...", he is referring to the Sidney Lumet's upcoming Network (1976) (which was released in 1976), earning its writer another Oscar.