Toby Jones's character Arthur P. Jacobs, Marilyn Monroe's then publicist, later became well known as the producer of Doctor Dolittle (1967), Planet of the Apes (1968) and its sequels and Goodbye, Mr. Chips (1969).
The notebook that Arthur Miller wrote and that Marilyn was seen crying over is most likely his initial draft of his play "After the Fall", which features a character that was a parody of Monroe. The play remains one of Miller's most unpopular works.
In the opening sequence, Marilyn appears singing "Heat Wave" in the screen of a movie theater. She sang that Irving Berlin song in There's No Business Like Show Business with a totally different set and costumes.
What happened to Colin Clark after the events of this movie?
He went on to have a successful career in film and television making. After retiring from filmmaking in the 1980s he became an author whose books included "My Week with Marilyn" and "The Prince, the Showgirl and Me," both of which form the basis for this film. He died in 2002 at the age of 70.